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

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

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