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. Do not change your system units unless you have unacceptable viewport behavior.
You should reset the system unit if you are working on a scene that is so large or so small that the software can no longer measure distances accurately using the default unit scale.
Tip: If you find you have slow viewport panning or zooming, try resetting the system units.
You change this value in Customize > Preferences > Preferences dialog > General tab > System Unit Scale group. Controls there are designed to help you evaluate the limits of accuracy when you change gmax system units.
The primary benefit of resetting the system units is that the viewports have a limited precision. Changing the System unit scale will allow better viewport display. (Z-buffering, clipping planes, zooming, etc.) If you are modeling a large city, for example, you may have many millions of inches; changing the system unit scale to feet will keep the number down in the thousands.
Warning: Do not reset the system unit unless you have a clear need to do so.
See also
Procedures
To change units to feet and inches:
Turn on US Standard in Units Setup.
Choose Feet or Inches as Default Units.
Select from among the choices on the drop-down list.
If you want feet, choose how the inches will appear, as fractions or decimal.
If you choose Fractional Feet or Feet w/ Fractional Inches, choose the fraction on the drop-down list to the right.
To enter fractions in numeric fields:
When you enter fractions in numeric fields, they are converted to the correct units. For example, if units are set to Feet w/ Decimal Inches, and Default Units is set to Feet, type 37/45 and press ENTER for the result 0'9.867", or 37/45'.
Note: 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:
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.
Interface
Click one of the option buttons (Metric, US Standard, Custom, or Generic) to activate its settings.
Metric: Click the list and choose a metric unit: Millimeters, Centimeters, Meters, Kilometers
US Standard: Click the list and 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.
Fractional Inches
Decimal Inches
Fractional Feet
Decimal Feet
Feet w/ Fractional Inches
Feet w/ Decimal Inches
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: This is the default option (one inch) and is equal to the system unit used by the software.