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Drawing Scales

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Blueprint drawings are typically drawn in

  • 1:20, 1:50 or 1:100 (SI-units)


  • 1/4" or 1/8"  (Imperial units, US)




To scale a SI-drawing

  • multiply the measurement on the drawing with the denominator

where the denominator is the number after the colon.

Example - Blueprint Drawing Scale 1:50

An actual length of 1 cm is measured on a 1:50 blueprint floor plan. The physical length can be calculated as

(1 cm) 50 = 50 cm

Imperial Units - US

A 1/4" scale means that each 1/4" (inch) on the plan counts for 1' (feet) of actual physical length.

To scale a blueprint in imperial units to actual feet

  • multiply the measurement on the drawing (in inches decimal equivalent) with the denominator

where the denominator is the bottom number.

Example - Blueprint Drawing Scale 1/4"

An actual length is measured to 1-3/8" on a 1/4" blueprint floor plan. The physical length can be calculated as

(1-3/8 inch) 4 = (1.375 inch) 4

= 5.5 feet

= 5' 6"


Commonly Used Drawing Scales


  • 1:1
  • 1:5
  • 1:10
  • 1:20

Component Drawings, Assembly

  • 1:20
  • 1:10
  • 1:5

Floor Plans, General Arrangement (GA)

  • 1:40
  • 1:50

Location Plot Plans

  • 1:80
  • 1:100
  • 1:200

Location Plat Plans

  • 1:500

Block Plan, City Maps and larger

  • 1:1000
  • 1:1250
  • 1:2500

Ordnance Survey Maps

  • 1:100000
  • 1:50000
  • 1:25000
  • 1:10000
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Related Topics


Basic engineering data. SI-system, unit converters, physical constants, drawing scales and more.

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