Tool
Architectural scale calculator
Pick the drawing's scale, type a length measured on the paper with a ruler, and read the real-world length. Or go the other way to find how long a wall should be on the sheet. Covers the architectural, engineering and metric scales, and any custom ratio.
Ratio 1:48. 1 in on the drawing = 4 ft; 1 cm on the drawing = 0.48 m.
From the drawing to real life
Real length
4' 0"1.22 m
From real life to the drawing
On the drawing
2.5 in63.5 mm
How scale conversion works
A drawing scale is a ratio between a length on the sheet and the same length in the building. The ratio 1:48 is the architectural scale 1/4″ = 1′-0″: a quarter inch on paper is twelve inches in the building, and 12 ÷ 0.25 = 48. To convert, multiply the drawing length by the ratio: 2.5 in on a 1/4″ = 1′ plan is 2.5 × 48 = 120 in, or 10 ft. To go back, divide: a 14 ft wall is 168 in ÷ 48 = 3.5 in on the sheet.
Metric scales are already written as ratios. On a 1:50 plan, 36 mm on paper is 36 × 50 = 1,800 mm, or 1.8 m. The maths is the same whatever the units, as long as you use the same unit on both sides.
One trap: the ratio is only true at the sheet's original size. A 24 × 36 in sheet printed on 11 × 17 paper shrinks everything to about 46%, and 1/4″ = 1′ no longer holds. If you're working from a reprint or a scan, measure a dimension string you can read and work out the real ratio, or let PDF Measure calibrate it for you.
Common drawing scales
| Scale | Ratio | 1 in on paper = | 1 cm on paper = | Typical use |
|---|---|---|---|---|
| 1″ = 1′ | 1:12 | 1' 0" | 1.2 cm | Details, millwork |
| 3/4″ = 1′ | 1:16 | 1' 4" | 1.6 cm | Details |
| 1/2″ = 1′ | 1:24 | 2' 0" | 2.4 cm | Kitchens, baths, wall sections |
| 3/8″ = 1′ | 1:32 | 2' 8" | 3.2 cm | Sections, small plans |
| 1/4″ = 1′ | 1:48 | 4' 0" | 4.8 cm | Residential floor plans, elevations |
| 3/16″ = 1′ | 1:64 | 5' 4" | 6.4 cm | Larger floor plans |
| 1/8″ = 1′ | 1:96 | 8' 0" | 9.6 cm | Overall plans, larger buildings |
| 1″ = 10′ | 1:120 | 10' 0" | 12.0 cm | Site plans |
| 1″ = 20′ | 1:240 | 20' 0" | 24.0 cm | Site plans |
| 1″ = 30′ | 1:360 | 30' 0" | 36.0 cm | Site plans |
| 1″ = 40′ | 1:480 | 40' 0" | 48.0 cm | Site plans, civil |
| 1″ = 50′ | 1:600 | 50' 0" | 60.0 cm | Site plans, civil |
| 1″ = 100′ | 1:1200 | 100' 0" | 1.20 m | Site plans, civil, subdivision |
| 1:1 | 1:1 | 1" | 1.0 mm | Full size details |
| 1:2 | 1:2 | 2" | 2.0 mm | Details |
| 1:5 | 1:5 | 5" | 5.0 mm | Details |
| 1:10 | 1:10 | 10" | 1.0 cm | Details, joinery |
| 1:20 | 1:20 | 1' 8" | 2.0 cm | Details, kitchens and baths |
| 1:25 | 1:25 | 2' 1" | 2.5 cm | Details |
| 1:50 | 1:50 | 4' 2" | 5.0 cm | Floor plans, elevations |
| 1:100 | 1:100 | 8' 4" | 10.0 cm | Overall plans, sections |
| 1:200 | 1:200 | 16' 8" | 20.0 cm | Site plans, small buildings |
| 1:250 | 1:250 | 20' 10" | 25.0 cm | Site plans |
| 1:500 | 1:500 | 41' 8" | 50.0 cm | Site plans, master plans |
| 1:1000 | 1:1000 | 83' 4" | 1.00 m | Site plans, master plans |
| 1:1250 | 1:1250 | 104' 2" | 1.25 m | Location plans |
| 1:2500 | 1:2500 | 208' 4" | 2.50 m | Location plans, maps |
Architectural scales are written as a paper length equal to one foot; engineering scales as one inch equal to a number of feet; metric scales as a plain ratio. All three are just ratios, and the table shows the one each stands for.