To apply dimensions in paper space:

1. Click on a layout tab. Create a viewport and set its scale as desired. View all or part of the drawing through the viewport.
2. Use the MV command to lock the viewport. This prevents zooming and panning within the viewport; zooming changes the scale, which throws off the consistent scale of dimensions applied through the viewport.
3. Apply dimensions using any of the methods described below.

Dimensioning Using the DIM Command.

Type DIM at the command prompt; this invokes a special dimensioning prompt which responds to special commands including HOR (horizontal), VER (vertical), ALIGNED (diagonal), or ORDINATE (i. e., datum level). Generally, these commands apply dimensions by asking you to specify two “extension line origin” points (i. e., the points you are measuring between) and a “dimension line location.” ORDINATE asks for a “feature location” and a “leader endpoint.”

Linear dimensions.

Use the Annotate > Dimension > Linear command (or DIMLINEAR at the command prompt) to apply automatic linear dimension strings to a drawing.

Ordinate dimensions.

Use the Annotate > Dimension > Ordinate command to apply automatic datum elevations to an elevation or section drawing. (Note: To change the datum point, use the UCS command to define a temporary origin point for the coordinate system.)

“Quick Dimensioning” (QDIM and QLEADER).

Use QDIM to quickly apply a series of dimensions to selected objects. Use QLEADER to apply and control settings for leader (arrow) lines.

See also:

AutoCAD: Using Dimensions.

AutoCAD Tutorial: Dimensions. http://www.cadtutor.net/tutorials/autocad/dimensioning.php