# Using Units

Units are the key to connecting the three-dimensional world of 3ds Max with the physical world. You define the units you want to use from the Units Setup dialog.

Changing Display Units

When you change display units, 3ds Max displays measurements in the new unit for your convenience. All dimensions are displayed in the new unit. Essentially, you’re using a new "measuring stick." No object is changed in this process. As in the physical world, objects in the scene maintain their absolute size, regardless of how you measure them.

Type-In Entry

When you enter any dimension, 3ds Max always assumes the number you enter is expressed in the current units. You can also enter a series of numbers: 3ds Max then converts their sum into the current unit. Here are some examples that assume the current units are in centimeters:

• When you enter a dimension of 1’ (one US foot), it converts to 30.48cm.
• If you enter a series of numbers such as 14 286 175 (separated by spaces), the series is totaled to 475.0cm.
• If you enter 1’ 1 (one US foot and 1 centimeter), this is converted and summed into 31.48cm.

When you use US Standard as the display unit scale, you can select either feet or inches as the default for type-in entry. If you select feet and enter 12, the result is 12’ 0". However, if you enter 1’ 2, 3ds Max identifies the second digit as inches, producing 1’ 2" as the result.

In any unit system, you can enter fractional amounts. For example, assume you’re working in US Standard with feet as the default:

• If you enter 18/3, the result is 6’0".
• If you enter 18/3", the result is 0’6".
• You can specify units in a different system, and they are converted on the fly. For example, if you enter 18/3cm, the result is 0'2.362".

Understanding the System Unit

3ds Max keeps track of all measurements in its own internal system unit. No matter what kind of display units you use, measurements are stored in this absolute unit for storage and computation. The default system unit is defined as 1.000 inch. As long as the system unit is left at one inch, you can freely share models and change units on the fly with no effect on the underlying geometry. Except in rare circumstances, you never need to change this default scale. This means you can merge a model created with any standard unit into your scene at true scale.

You can change the system unit setting on the System Unit Setup dialog, available from the Units Setup dialog. Changing the system unit is recommended only if your scene has very small (less than one inch) or very large dimensions. See System Unit Setup Dialog for more information.

If you do need to change the system unit, change it before you create or import geometry. Do not change the system unit in an existing scene.