How to Set DIMSCALE

DIMSCALE, a system variable available in AutoCAD and several other CAD programs, is used to size dimensioning elements such as text, leader arrowheads, and extension line offsets. To see or change the DIMSCALE value for the current drawing, type DIMSCALE at the CAD program's command line.

What Should My DIMSCALE Be?

To determine your DIMSCALE value, you are effectively asking yourself this question: "If I printed this drawing onto paper and measured a real inch on the physical page, how many inches (or feet or meters) would that represent on the plan?"

The table on the left has DIMSCALE values for common drawing scales, assuming your drawing's base unit is an inch.

Methods and examples for determining the right DIMSCALE value for your drawing are explained below.

Finding Your Base Unit

First, you need to determine the base unit of your drawing—the length represented by a single unit of measurement. Architectural drawings typically use smaller units like an inch or centimeter, while site drawings typically use larger units like a foot or meter.

If you're not sure what your base unit is, follow these steps to find it:

1. Enter UNITS at the command line.
2. Make a note of your current Length Type setting, then set it to Decimal and press the OK button to save the change.
3. Enter DIST at the command line, then measure a length or distance that you know, such as the width of a door or parking space.
4. (Optional) If you changed the Length Type earlier, run the UNITS command again to return it to its previous setting.

Use the distance measured in step 3 to determine the base unit for your drawing. The following list uses the approximate width of a door as an example:

• Inch: 36 units
• Foot: 3 units
• Centimeter: 90 units
• Meter: 0.9 units

Finding Your Scale Factor

Once you know your base unit, you then need to convert your scale factor to that unit. Once you have your base unit on one side of the equation, the value on the other side is your DIMSCALE.

The examples below assume your base unit is an inch.

For a 1/8″=1′ scale factor, convert 1′ to 12″, which gives you 1/8″=12″. Then, multiply both sides by 8 to get 1″=96″. For a 1/8″=1′ drawing, use a DIMSCALE of 96.

For a 1″=20′ site plan, convert the 20′ to inches to get 1″=240″, resulting in a DIMSCALE of 240.

For a scale like 3/16″ = 1′, convert 1' to 12" to get 3/16" = 12". Then, multiply both sides by 16 to get 3" = 192". Finally, divide both sides by 3 to get 1″ = 64″, and therefore a DIMSCALE of 64.

If your base unit is a foot, you can use the same method as the above examples either by converting the scale so that one side of the equation is 1' instead of 1", or by dividing the final value by 12. Similarly, using the table of common DIMSCALE values at left, you can divide any of those values by 12 to get your DIMSCALE for a drawing with a foot base unit. The same logic applies to metric base units.