Customize menu > Units Setup > Units Setup dialog
The Units Setup dialog establishes the unit display method, giving you the choice between generic units and standard units (feet and inches, or metric). You can also create custom units, which are used whenever you create an object.
The units that you set up are used to measure geometry in your scene. In addition to these units, the software also uses system units as an internal mechanism. System units should only be changed before you create your scene or import a unitless file. Do not change the system unit in an existing scene.
You can also set the lighting units using this dialog.
It is important to note the distinction between System and Display units. Display units only affect how geometry is displayed in the viewports. System units determine the actual scale of geometry. For example, if you import a DXF file (unitless) containing a 1 x 1 x 1 Box, Autodesk VIZ could import the box’s dimensions in inches or miles, depending on the System unit. This can have a significant impact on your scene, which is why you should always set up the system unit before you import or create geometry.
To enter a fraction and a units specifier, place the specifier after the divisor. For example, type 17/5', but not 17'/5.
To convert between unit types:
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You can convert between unit types by entering any valid unit specifier, along with the number, and then pressing Enter.
The number is converted to the current unit display type. For example, if units are set to Meters, type 1/2 to get the result 0.5M. However, if you type 1/2' or 6" the result is 0.152M.
System Unit Setup—Click to display the System Unit Setup dialog and change the system unit scale.
Warning: Change the system unit value only before importing or creating geometry. Do not change the system unit in an existing scene.
Choose a unit scale option (Metric, US Standard, Custom, or Generic Units) to activate its settings.
Metric—Choose this option and then choose a metric unit: Millimeters, Centimeters, Meters, or Kilometers
US Standard—Choose this option and then choose a US Standard unit. If you choose a fractional unit, the adjoining list activates to let you select the fractional component. The decimal units require no additional specification.
The US Standards are as follows:
For the last two items, you can specify which unit is assumed when you enter a value in a numeric field and press Enter without including a units specifier, such as ' for feet or " for inches.
For example, if Feet is the default, typing 5 followed by Enter results in 5 feet. Typing 5" followed by Enter results in 0'5". If Inches is the default, typing 5 followed by Enter results in 0'5". Typing 5' followed by Enter results in 5 feet.
Custom—Fill in the fields to define a custom unit of measurement.
Generic Units—This is equal to the system unit used by the software.