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Scales Commonly Used in Blueprints

One of the questions we commonly receive, especially from Student Surveyors is how to read blueprints and interpret scales commonly used in Blueprints.

Blueprint drawings are typically drawn in 

  • 1:20, 1:50 or 1:100 (SI-units)

or

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

scales.

SI-Units

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

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

Details

  • 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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