How To Change My Unit Measurements In Blender?
3D modeling applications can be used to create accurate representations of real-world objects. But for them to be truly accurate, the models need to be using the correct values for their dimensions. Dimensions play an important role in architecture, physics simulations, and in 3D printing.
You can change the active units of measurement by going to Properties > Scenes > Units, and changing the unit system to the measurement system that you want to use. Then change the length attribute to best represent the size of the objects that you are trying to create. For example, a pencil would be best suited with centimeters and a large space station could use kilometers.
It is very easy to miss for a beginner and while it does not matter so much when you are simply creating objects for a scene render in Blender itself. Problems can occur if the unit of measurement is too large or too small for an external purpose like game design or 3D printing.
What Are Blender Units And Why Are They The Default?
Blender Units are the default system of measurement that Blender uses if no real-world systems have been assigned. They are easy to work with for beginners and can be used for creating objects and scenes of various sizes.
The Blender unit most closely resembles metric meters in terms of the actual size of the objects that are created. If you open up the side panel in the 3D viewport, you will be able to see which unit system is being used for the current project by looking at the values for the location, rotation, and scale of the selected object.
Side Panel Blender Units
If Blender units are applied as the system of measurement, then you will only see float numbers for location and dimension.
Even in this system, you are still using degrees for your rotational values but none of the other Unit attributes can be changed.
- Unit Scale (Slider)
- Separate Units (Checkbox)
- Rotation
- Length
- Mass
- Time
- Temperature
If you are using Blender units as your system of measurement, then the unit system option will appear as none and all of the attributes apart from the rotation will be greyed out and nonselectable.
You can change your unit system here to either metric or imperial. If you are not sure about which to choose, In Europe, the metric system is used to calculate in millimeters, centimeters, etc. While America uses the imperial system for inches, feet, yards, etc.
Blender Unit Systems Location
When Should You Change Your Unit System And Parameters?
If you are designing a scene specifically for rendering within Blender, then changing the unit system will not really make a difference so long that the objects themselves are the correct size when compared to each other. Here the standard Blender units system will do the job nicely.
Where the scale of the object becomes important is in any situation where the 3Dmodels will be exported to another program.
Metric Unit options
For example, a common use of Blender is to create objects for video games, meaning that the objects will need to be exported to a game engine.
Game engines will have their own systems for object behavior, physics simulations, etc. And so the object that we export will need to be the correct size and scale for those physics simulations, otherwise, the behavior may not be what we expect.
Other situations where you will need to make changes to your unit system will be for creating physical products through architecture, manufacturing, and 3D printing.
Basically, if the purpose of a model is to be used exclusively within Blender, then you do not need to change the unit settings. If the purpose is external, like in game design, then the unit system becomes much more important.
What Can Go Wrong If You Do Not Change Your Unit System?
That depends on what you are trying to do with your object. As mentioned above, in game design the scale of the model should be correct for the scene that it needs to be imported into. Incorrect sizing can be adjusted and corrected in the game engine itself, but it is better to make sure that your dimensions are correct before exporting from Blender.
This way you know that there are fewer things that can go wrong with an asset when you begin to use the model for animations, physics simulations, etc.
Another thing to be careful of is the scale value. If you look at the side panel in Blender you will notice that the scale values remain the same regardless of the unit system that was used. This is because the scale is relative to its original size, and the dimensions are the true values for the size of the object.
When these scale values are set to something other than one it can cause incorrect behaviors even if the unit system and length were correct.
To apply your scale, select the object in Blender and use the hotkey of Control + A to bring up the apply menu, then select rotation and scale to apply those transforms.
How Can The Unit Scale Value Help In Modelling?
The unit scale is a universal scale system that you can use to increase or decrease the size of your models all at the same time.
Let’s say you began a project creating a low poly city with buildings of various shapes and sizes, mostly built around cube objects.
You set up the look of your scene so that everything looks to be the correct size. However, you then notice a problem when you check the transforms.
Your tallest building is only 12 meters high when it should be 120. All of the buildings look right, but they are all smaller than what they need to be.
Instead of having to go in and manually change the scale of each object, you can adjust the unit scale value in the properties panel. So in this case, we can increase the unit scale to 10 to make all the objects 10 times the original size. You can double-check this by looking at the object’s dimensions.
Separate Units
Another useful tool here is the separate units option found just below the unit scale. When this option is ticked the dimensions are split to become easier to read. For example, 20.1 meters will become 20m 10cm, and so on.
Keep in mind that adjusting the unit scale works for the objects that are currently in your scene. Adding a new object after changing the unit scale will still result in that object having its original dimensions, meaning it may appear much larger or smaller than the rest of your scene.
Does The Unit System Effect Clipping?
Clipping is the effect where the viewport cuts out detail after a certain point, whether that be from zooming too far in or too far out of your scene.
You can access the clipping values by pressing N to open up the side panel, then going to View (Tab) > View and changing the clip start and clip end values.
Clip Start And End
If you are using the metric system with meters as the length, then the lowest value before clipping occurs will be 1cm, while the highest point will be 1km.
Note that the clipping values are dependent on the unit scale value, so changing the unit scale will alter the start and end values in real-time.
Thanks For Reading Our Article
We hope that you enjoyed reading our article on the unit systems in Blender. Below we have gathered a shortlist of other articles we think you may be interested in.
The Different Ways That We Can Separate Objects?
There are a variety of ways in which we can manipulate the geometry used to construct our mesh objects. There are also several tools that can be used to manipulate
How To Join Multiple Objects Together?
Before learning how to redesign mesh objects, it is often recommended to learn the tools that affect the objects, namely the tools used in Object mode. One such tool is
How To Parent One Object To Another?
When working in object mode, we have far more variety than simply manipulating the transforms of our selected objects. For example, we can duplicate the objects or reposition them using
Еденицы измерения
Возможно.
Это делается изменением шага сетки окна 3D Viewport’a: View/View Properties.
В Wiki это звучит так:
The 3D Viewport’s grid represents Blender Units (BU). A BU can be as large as you would like it to be: an inch, a centimeter, a mile, or a cubit.
(http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Blender_Windowing_System)
Что в переводе означает:
Сетка 3D Vieport’a представляет собой единицы измерения Blender’а (BU). BU может принимать любые значения, будь то дюйм, сантиметр, миля, или кьюбит.
Как поменять метрическую систему в blender
Текстовое поле и поле поиска.
Текстовые поля имеют закруглённую прямоугольную рамку и, возможно, значок и/или текст внутри рамки. Текстовые поля хранят текстовые строки и предоставляют средства для редактирования текста с помощью стандартных сочетаний клавиш редактирования текста .
Для текстовых полей со значком и всплывающими окнами см. Data ID .
Числовые поля
В числовых полях хранятся значения и единицы измерения.
Первый тип числового поля показывает треугольники, указывающие влево (<) и вправо (>) по сторонам поля, когда указатель мыши находится над полем. Ползунки, второй тип числового поля, имеют цветную полосу на заднем фоне для отображения значений в диапазоне, например, процентные значения.
Значение можно изменить несколькими способами:
Чтобы изменить значение поэтапно, нажимайте ЛКМ по маленьким треугольникам (доступно только для первого типа поля). Вы также можете использовать Ctrl — Колесо при наведении курсора на поле, чтобы отредактировать значение.
Чтобы изменить значение с помощью мыши, зажмите ЛКМ и перетащите влево или вправо.
Удерживайте Ctrl для привязки к дискретным шагам при перетаскивании или Shift для более точного ввода.
Ввод с клавиатуры
Нажмите ЛКМ или Return , чтобы ввести значение, набрав его с клавиатуры.
При вводе значений с клавиатуры, числовые поля работают также, как и текстовые поля:
Для применения изменений нажмите Return или ЛКМ за пределами поля.
Для отмены нажмите Esc или RMB .
Для перехода к следующему полю нажмите Tab , для перехода к предыдущему нажмите Shift — Tab .
Нажмите Minus , наведя указатель мыши на числовое поле, чтобы инвертировать значение (в версии 3.0 не работает).
Редактирование нескольких значений
Редактирование нескольких значений.
You can edit multiple number fields at once by pressing down LMB on the first field, and then dragging vertically over the fields you want to edit. Finally you can either drag left or right to adjust value with the mouse, or release the LMB and type in a value.
Ограничение значений
Большинство числовых значений ограничены диапазонами значений «soft limit» (мягкий предел) и «hard limit» (жёсткий предел). Изменение значений путем перетаскивания мышью ограничено диапазоном значений «мягкого предела». Ввод с клавиатуры позволит использовать более широкие диапазоны значений, но не более «жёсткого предела».
Expressions
Вы можете вводить математические выражения в любое числовое поле. Например, введите 3*2 или 10/5+4 вместо 6 . Можно использовать даже такие константы, как Пи (3.142), или такие функции, как sqrt(2) (квадратный корень из 2).
Эти выражения вычисляются Python; все доступные математические выражения см. в Cправочнике по математическим модулям.
Выражения как драйверы (управляемые выражения)
Вы можете захотеть, чтобы ваше выражение было переназначено после его ввода. Blender поддерживает это с помощью Драйверов (функция системы анимации).
Выражения, начинающиеся с # , имеют особое назначение. Вместо оценки значения и отбрасывания выражения, к свойству добавляется драйвер с введенным выражением.
The expression #frame is a quick way to map a value to the current frame, but more complex expressions like #fmod(frame, 24) / 24 are also supported.
Это просто удобный ярлык для добавления драйверов, который также можно добавить через меню, нажатием ПКМ .
Единицы измерений
As well as expressions, you can specify numbers and units. If no unit is given, then a default unit is applied. The unit system can be changed in scene settings .
Вы можете использовать либо аббревиатуру единицы измерения, либо полное название после значения.
Metric & Imperial Units in Blender
Blender provides three distinct types of unit that can be used to measure objects (distance) in a Scene; "None", "Imperial" and "Metric". Although relatively self explanatory in terms of what they represent, their use does come with some caveats the user needs to be aware of, which depends particularly upon the version of Blender being used.
Contents
Resources
With this in mind the following discusses where to find these settings and how they can be used within Blender to give content a real world measurement context. A basic understanding of Blender is recommended but not specifically required to get the most from the below.
The Units system ^
As briefly touched upon in the introduction, the distance and/or angle between two points or edges, or the area attributed to a given surface, can be measured relative to a choice of three distinct ‘units of measurement‘, "None", "Metric" and "Imperial". Each ‘type’ of unit has its own set of options organised under Blenders main "Units" sub-system, which itself can be found within "Scene" Properties, and breaks down as follows;
"None" represents simple ‘unit’ based measurement.
"Metric" represents "millimetres", "meters" etc.
"Imperial" represents "inches", "foot", "mile" etc.
Design note: the ‘unit’ of Blenders default system "None", whilst similarly ‘decimal’ in nature to "Metric", has no meaning beyond its face value. In other words, by itself, a measurement of "1000" means one thousand units and nothing more. Whereas "1000" within the "Metric" system might be referring to any manner of unit types; is that one thousand metres, kilometres, nanometres etc.
In essence the way the "Units" system works is two-fold; 1) the unit type selected defines what each unit of measurement means (gives context to numerical values assigned to various properties and settings); and 2) arranges the appearance of the Grid in the 3D View to use a set of predetermined characteristics that alter the way major and minor cells are divided and scaled relative to objects in the scene and the unit of measurement used. What this means is that in selecting one or the other "Metric" or "Imperial" systems ("None" behaves as "Metric" but without the ability to set meaningful sub-selection or unit types), the grid is changed to display each cell larger or smaller depending upon the type of measurement selected ("Metric", "Imperial", "None"), and the unit represented ("Inches", "Yards", "Meters", "Miles" etc.) — the grid set to yards for example, displays smaller cells than would be seen under meters due to differences between the two unit types.
Design note: Blender’s measurement system in it’s entirety is largely composed of the ‘unit of measurement’ properties and the Grid displayed in the 3D View; the former sets the latter, with the latter acting as a visual representation of the former.
The default Scene when Blender is loaded showing "Render" properties selected — note that the actual options and settings visible will vary depending upon the version of Blender used (Blender 2.71 shown)
Clicking the "Scene" button reveals a collection of properties and options attributed to the scene itself, including "Units", which by default displays "None", meaning measurement is simply an expression of a ‘unit’ (the above is shown in Blender 2.71 but applies to Blender 2.56 and above)
In Blender 2.50 through to Blender 2.55 the appearance of "Units" properties differs slightly but the user is still able to select the appropriate type of unit system wanted at the click of a button
Selecting a Units option ^
As discussed above, after clicking "Scene" properties the "Units" sub-section presents three options; "None" (the default), "Metric" and "Imperial". When each is selected a different set of properties appear based on what units are to be represented and used;
"None" presents no additional options.
"Metric" includes additional buttons for "Degrees" and "Radians", a "Scale:" value and an option to "Separate Units" (checkbox).
"Imperial" includes additional buttons for "Degrees" and "Radians", a "Scale:" value and an option to "Separate Units" (checkbox).
Design note: when selecting "Imperial" the 3D Views Grid, when viewed in Perspective mode, tends to resize quite significantly because each cell represents a much smaller unit of measurement, "foot"; set to "Meters" each ‘minor’ grid cell represents a 1m x 1m area, a ‘major’ grid unit then representing a 10m x 10m grid of such cells; whereas set to "Imperial" each ‘minor’ cell is a 1ft x 1ft area, a ‘major’ grid then represents a 10 square foot area, which is significantly smaller than 10 square metres (this change/difference may not be visible in all versions of Blender).
Selecting "None" for "Units" no additional options are available because the unit itself, i.e. the distance its supposed to represent, is determined by Grid settings in "Transform" properties
Selecting "Metric" reveals an additional set of properties; a "Scale:" value, two options to determine how rotational values are to be treated and "Separate Units" (generally speaking these options are available in all versions of Blender but may be grouped or positioned in slightly different locations as is the case for Blender 2.50 through to Blender 2.55 — Blender 2.71 shown)
Selecting "Imperial" similarly reveals an additional set of options; "Scale:", the same two "Degrees" and "Radians" buttons and the "Separate Units" option (again as with "Metric", the position and grouping of these options may differ to other versions of Blender as is the case for Blender 2.50 through Blender 2.55 — Blender 2.71 shown). Note additionally the significant change in size to the Grid visible in the 3D View as a result of it using much smaller units of measurement, "Feet" instead of "Meters" (this change/difference may not be visible in all versions of Blender)
Default Object, Units and Grid size ^
Alluded to in the above, switching between "Metric" (or None) and "Imperial" results in quite a significant change to the Grid. This is largely because the different systems use quite distinct base units for measurement; for "Metric" this is "Meters"; for "Imperial" it’s "Feet". In other words each minor grid cell is either 1 x 1 metres under the Metric system, or 1 x 1 foot using Imperial. Whilst this isn’t problematic in of itself, the difference has an unintentional consequence on the default Scene Cube; switching from Metric (or None) to Imperial, it’s slightly too big; going the other way, switching from Imperial to Metric (or None), it’s too small.
Design note: this assumes Units are switched after Blender and the default Scene contents have loaded, but before switching between the unit systems.
By default the Scene Cube appears centred on the Grid as a 2 x 2 x 2 unit object, "unit" being the base measurement. When switching to "Metric" this same cube is measured as a 2 x 2 x 2 metre object — "Metric" and "None" directly correlate. In Imperial because the based unit is "feet", it should appear as a 2 x 2 x 2 foot object but it doesn’t, its size remains relative to its original dimensions, now a 6′ 6" x 6′ 6" x 6′ 6" cube (1 metre equals 3′ 3", so the cube, originally being 2 metres, is 2 x 3′ 3" or 6′ 6" across). In other words its size doesn’t (always) change when switching between None/Metric and Imperial to properly reflect the selected Units system. This is generally true of all content, which remains true-to-size irrespective of the unit of measurement set.
Design note: this is also true in reverse; when working in "Imperial", and switching to either "Metric" or "None", the opposite problem occurs where distances are then proportionally too small because of the up-scale in unit size; items then have to be re-scaled upwards to match the new, larger grid.
The upshot of this is that when starting a new project, clearing (deleting) the default cube and loading in a new one might be necessary. This places into the Scene an Object that’s correctly proportionate relative to the underlying base unit of measurement. To add a new object, with the cursor over the 3D View, press "Shift+A" to access the "Add" menu options, select the object required (which will be added at the 3D Cursors location). Alternatively click the "Add" menu option in the 3D View Header and select an item from the list. Or from the Tool Shelf on the left of the 3D View, click the "Create" tab then on a button representing the required object.
Design note: when reloading the start-up file, unless "User Preferences" have been changed, the Scene that loads is set to use "None" units of measurement with the default Cube sized appropriately. Adding Objects loads them relative to the Cursor location so that may need to be reset or moved beforehand.
The default Scene showing the default Cube in transparent grey so the ‘corrected’ cube for Imperial measurement can be seen through it, highlighting the difference between the two — the red ‘target’ area indicates the relative size of the "Metric" base unit being "Metres"
Similarly the same objects shown as above with the red ‘target’ area indicating the much smaller unit for Imperial measurement, "Feet" — preference should be paid to clearing the file and loading in an appropriate object when switching, which Blender automatically resizes relative to the base unit used by the system
Shown in Perspective mode the white target area highlighted indicates the size difference measured in metres — note the ‘unit’ reference top left of the 3D View — "Meters"; note also the transparent cube representing the defaults fits exactly within the Grid lines indicating its 2 x 2 x 2 metre size
Using " Imperial" measurement, the central cube is the correct ‘default’ that should be loaded as it is also 2 x 2 x 2, but in ‘feet’ not ‘meters’. Note the Grid, relative to the original object, clips, whereas the smaller object fits exactly within as should be expected
Units Scale/Size ^
Along side the establishment of each systems base ‘unit’, are each their respective "Scale:" values. What this does is allow different levels of measurement accuracy to be defined within the bounds of the aforementioned system base unit. In other words in wanting to measure ‘Inches‘, the default value of "Scale: 1.000", which represents ‘feet’, needs to be decreased, for ‘Miles‘ it would be increased and so on. For example when "Imperial" sets the default unit to "1 foot" with "Scale: 1.000" this means the value has to be changed so that;
0.083 = 1" (one inch).
1.000 = 1′ (one foot).
3.000 = 1yd (one yard).
Design note: in Blender 2.50 through to Blender 2.56 the above unit values do not correlate with Blender 2.56 and after due to a differences in the way the system registers the base unit. In the earlier versions (2.55 and below) measurement was seen relative to "Scale: 1.000" being representative of 1 metre regardless of the unit system. In other words this means Imperial unit calculations are done relative to dividing metres, not feet, by the decimal version of an Imperial unit of measurement (see below).
When changing the "Scale:" value attributed to the use of Imperial Units, the relative size of the default Scene Cube object changes — although this is generally not seen as the object itself doesn’t change insomuch as its "Dimensions:" (in 3D View Properties, "N") are altered to match the grid and unit scale
Similarly when "Metric" sets the base unit to "1 meter" and "Scale: 1.000" this means;
0.001 = 1mm (one milimetre).
0.010 = 1cm (one centimetre).
0.100 = 1dm (one decimetre/ten centimetres).
1.000 = 1m (one metre).
1000.000 = 1km (one kilometre).
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inch — 2" x 2" x 2".
-
feet — 2′ x 2′ x 2′.
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yard — 2yd x 2yd x 2yd.
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centimetre — 2cm x 2cm x 2cm.
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metre — 2m x 2m x 2m.
-
kilometre — 2km x 2km x 2km.
The upshot of this change is to make sure the unit scale is set correctly before starting a project otherwise objects that might actually need to be large, but built relative to a smaller scale, may inadvertently have their respective dimension values resized to suit after-the-fact alterations to the Scale property.
Shown is the relative size of the default cube as seen when the "Scale:" value is changed to alter the unit of measurement — larger values cover larger distances, smaller values smaller distances. Again, when "Scale:" is changed the object itself is not modified insomuch as its general "Dimension:" are updated to suit the base unit System and type, i.e. "Metric" and "Metres"
To change the "Scale:" value simple left-click in the input field, delete any values as might be present and type. Press Enter to confirm the change (or click elsewhere on screen). Upon doing this the 3D View’s Grid and other settings will update.
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1 inch = 0.0254 metres.
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1 foot = 0.3048 metres.
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1 yard = 0.9144 metres.
In Blender 2.50 through to Blender 2.55 the base unit of all measurement systems is "1 unit" (large blue/grey cube shown above), which translates directly to "1 metre". This subsequently means scaling, by Grid or "Units" properties has to be calculated relative to the decimal unit/metre when using Imperial measurements
Top down view showing the difference between base units. From Blender 2.56 changing to "Imperial" units of measurement adjusts the base unit relative to being "1 foot". This means ‘inch’ and other Imperial measurements can be calculated properly relative to Imperial units (although calculations are still required to be carried out in ‘decimal’)
View Properties & Units ^
Secondary to "Scale:" in "Scene" properties are a set of options available in "Display", a subsection of the 3D View’s "Properties" tool shelf overlay. Here three settings allow for a slightly different way to control Grid sizing; "Lines:", "Scale:" and "Subdivisions:". Having said this however, the availability of the options depends on the "Units" type selected — when using "Metric" and "Imperial" measurement "Subdivisions:" is greyed out, although still usable despite both unit systems typically relying on predefined cell sizes. To access the options, with the mouse over the 3D View, press the "N" key, or from the views Header menu click "View » Properties". Once open scroll down to the "Display" sub-section to view/edit the available options (click the small triangle to the left of the heading to expand if not initially visible).
Design note: although "Subdivisions:" is greyed out to indicate its generally non-functional, it does work. This means that aside from using "Scale:" in "Scene" properties to set the base unit, "Subdivisions:" can still be used to define the grid for better display (and use) of the unit being used. The Grids appearance differs slightly when displaying this in Perspective and Orthographic modes.
Additional options for unit management can be found in the 3D Views "Properties" tool shelf overlay. Here "Lines:", "Scale:" and "Subdivisions:" can be used to change the way the Grid appears such that its cells can be altered to account for larger or smaller units of measurement against the default Unit ‘types’
When either "Metric" or "Imperial" units are active the "Subdivisions:" property is automatically semi-disabled and greyed-out — it can still be used to further/better define units however
Similarly "Subdivisions:" is semi-disabled when using "Imperial" Units — the setting can be used to modify the predefined defaults based on the "Scene" properties "Scale:" value depending on the unit of measurement required (is generally preferred because Imperial use divisions of odd unit counts — a foot being divided by twelve instead of ten for example
Although "Lines:", "Scale:" and "Subdivisions:" are available universally (notwithstanding the greyed-out caveat mentioned above), they are generally of more use when using Blenders default Units system, "None", largely because it doesn’t use any predefined Grid scaling (certainly not in the same way as "Metric" and "Imperial" units).
To change the Grids size in the 3D View left-click the "Scale:" input field and type a new value depending on requirements — the default "Scale: 1.000" equates to one metre, so scaling up "10" would allow models to be build over much larger distances, "0.25" much smaller. Press Enter or click elsewhere on screen to confirm.
Design note: when larger scales are used, although they facilitate being able to build over greater distances, the increased scale also has a similar affect on Grid snapping when manipulating objects, making it somewhat clumsy where smaller details and objects need to be manipulated — it’s often preferable to build (details) at normal scale and increase afterwards.
Using "Scale:" each Grid cell is increased in size but not dimensions, in other words each cell shown above is 1 x 1 x scale 2 and not 2 x 2 — the dimensions of the cell don’t change, similar in fact to the way the default cube can be rescaled but it’s root dimensions remain the same (warranting the use of "Apply" to set the object data to its new sizing)
To change the number of divisions each Grid cell contains amend the "Subdivisions:" value as needed — the default is "Subdivisions: 10", which can be interpreted as ten individual units, or using the Grid to represent ‘metres’ without setting "Metres" in "Scene" properties, ten blocks of ten centimetres per each larger Grid and so on, changing the value alters the number of divisions and thus the distance each might then represent.
Design note: as mentioned briefly above, when using "Metric" or "Imperial" units of measurement "Subdivisions:" is greyed out, but not disabled. This allows it to be used to override any default or predefined Grid divisions as might be used by the system based on "Scene" properties and "Scale:" found there.
In changing "Subdivisions:" it’s possible to set the Grid up so its sub-cells change in relative number and size. This can be used to defined different levels of snap, or units of measurement — if the default "Scale:" is set to "1.000" unit, each subdivision represents 1/10th of that (or blocks of ten centimetre if the base-unit is 1 metre)
To change the size or area the Grid occupies in the 3D View edit the number of "Lines:" setting — the default is "Lines: 16" which shows the Grid occupying a certain percentage of screen real estate; increasing or decreasing "Lines:" changes this so measurement can be assessed relative to the Grid area and respective object size over greater or lesser extents.
Design note: the "Lines:" property only affects the 3D View when in Perspective mode, in Orthographic, changes do not outwardly make any difference (the gird is infinite in Orthographic view).
Using "Lines:" the grid can be expanding or reduced in size relative to the number of grid cells are seen. The default value of "16" allows for quite localised objects to be built of about 160 units before the grid would need to be expanded further, setting a new limit
Separate Units ^
Measurement in Blender is decimal in character and calculated relative to a whatever base unit is being used/has been set. In essence what this means is that by default numerical values always appear as decimal divisions of whole numbers. For example in "Metric" a measurement of "6.5000" is representative of six and a half metres, ‘metres’ being the base unit, or in "Imperial" six and a half feet, ‘feet’ being that systems base unit. For clarity Blender has the ability be better define the unit hierarchy so the aforementioned "6.5000" becomes "6m 50cm" under the "Metric" system or "6′ 6"" under "Imperial". This is done activating the "Separate Units" property. To do this, in "Units" simply click the checkbox to the left of the sub-heading to activate.
Design note: depending on the actual value, fractions (numbers ‘behind’ a decimal point) may still appear as decimally place figures relative to using "Separate Units" even when the feature is active, more so for "Imperial" units which would otherwise result in tiny (decimal) fractions, and mean additional math calculations be performed under certain circumstances for accuracy.
In "Imperial" mode units of measurement values are generally relative to the base unit, feet. This results in decimal placements for some values which can be confusing — "6.5" feet is actually six feet six inches not six feet five
With "Separate Units" active, values are split based on their hierarchy; for example in "Imperial" units will be split into "feet" and "inches" (values smaller than the smallest unit may still appear as decimal fractions because Blender cannot correctly display Imperial type fractional increments, i.e. 4/5ths, 7/16ths etc.). Note that "Lines:" and "Scale:" remain unchanged because their values are not expressly units of measurement, and that "Subdivisions:" is greyed-out (but not disabled)
In "Metric", units similarly display as simple decimal fractions by default
With "Separate Units" activated, values are again split into their respective hierarchical relationship, in this instance metres and centimetres. Similarly to "Imperial" properties above note that "Lines:" and "Scale:" remain unchanged with "Subdivisions:" being greyed-out (but still usable)
Valid Units of measurement ^
When selecting either Metric or Imperial Units Blender defaults to using metres or feet as their respective baselines which can be changed up or down depending upon the "Scale:" value set in "Scene" properties — making the value larger would set ‘kilometres’ or ‘miles’, smaller and it would be ‘inches’ and ‘centimetres’. In addition to this the unit type is further highlighted by the presence of an appended identifier — "m" for metres, "cm" for centimetres, "‘" for feet and """ for inches and so on, or combinations therein depending on the fraction value and whether "Separate Units" is active. In other words valid units of measurement (and scale) are typically indicated as follows (most commonly used);