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.

Calculating Scale Factor

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 

Architectural Scales

Drawing ScaleScale Factor Viewport ScaleDecimal Scale
1/16" = 1'-0"1921/192xp.0625" = 1'-0"
3/32" = 1'-0"1281/128xp.09375" = 1'-0"
1/8" = 1'-0"961/96xp.125" = 1'-0"
3/16" = 1'-0"641/64xp.1875" = 1'-0"
1/4" = 1'-0"481/48xp.25" = 1'-0"
3/8" = 1'-0"321/32xp.375" = 1'-0"
1/2" = 1'-0"241/24xp.50" = 1'-0"
3/4" = 1'-0"161/16xp.75" = 1'-0"
1" = 1'-0"121/12xp1" = 1'-0"
1 1/2" = 1'-0"81/8xp1.5" = 1'-0"
3" = 1'-0"41/4xp 3" = 1'-0"

Engineering Scales

Drawing ScaleScale FactorViewport Scale
1" = 10'-0"1201/120xp
1" = 20'-0"2401/240xp
1" = 30'-0"3601/360xp
1" = 40'-0"4801/480xp
1" = 50'-0"6001/600xp
1"= 60'-0"7201/720xp
1" = 70'-0"8401/840xp
1" = 80'-0"9601/960xp
1" = 90'-0"10801/1080xp
1" = 100'-0"12001/1200xp
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