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)
- 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
Component Drawings, Assembly
Floor Plans, General Arrangement (GA)
Location Plot Plans
Location Plat Plans
Block Plan, City Maps and larger
Ordnance Survey Maps