# CAD Scale Factors

For simplicity and clarity, CAD users draw buildings at full scale.  For instance, when drawing a door in CAD, the door would be 3 feet wide and 7 feet tall.  However, since these drawings get placed on sheets of paper that are much smaller, a scale factor is required so that the final drawing has a usable conversion factor. This is where CAD Scale Factors come into play.

You will notice that the Viewport Scale in the charts below indicate a scale with the suffix XP. The suffix is AutoCAD nomenclature for changing the scale within a viewport. For instance, you would be in paper space on a sheet, then you would enter model space within the viewport, then you would type Z or Zoom and enter 96xp to scale the drawing to 1/8" = 1'-0" in paper space. Said a different way by Autodesk, "You can change the view scale of the viewport by using the XP option of the ZOOM command when model space is accessed from within a layout viewport."

## Calculating CAD Scale Factors

To convert an architectural drawing scale to a scale factor:

1. Select the desired scale.  1/8" = 1'-0"
2. Invert the fraction and multiply by 12. 8/1 x 12 = Scale Factor 96

To convert an engineering drawing scale to a scale factor:

1. Select the desired scale. 1" = 20'
2. Multiply the feet by 12.  20 x 12 = Scale Factor 240

## Engineering Scales

Be sure to check out our article, Converting Between Drawing Scales, if you need to manually change the scale of a drawing or object.

Article Updated: February 3, 2024

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