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Architectural Scale Converter
Convert a real dimension to its size on a drawing, or measure a drawing and get the real size, at any architectural, engineering or metric scale. The scale factor for every common scale is listed below.
Architectural scale converter
Scale factor
1:48
On the drawing
3.125"
On the drawing
79.4 mm
Real size
12'-6" · 3.810 m
How to use a drawing scale
A drawing scale says how much smaller the drawing is than the building. At 1/4" = 1'-0", every quarter inch on paper is one foot in real life. The scale factor is the number you divide or multiply by: at 1/4" scale it is 48, because one foot (12 inches) is 48 quarter inches.
Real size ÷ scale factor = drawing size. Drawing size x scale factor = real size. A 12'-6" wall at 1/4" scale is 150 ÷ 48 = 3.125 inches long on the drawing.
Architectural scale factor chart
| Scale | Ratio / factor | Typical use |
|---|---|---|
| 1/16" = 1'-0" | 1:192 | Large building plans, site plans |
| 3/32" = 1'-0" | 1:128 | Large floor plans |
| 1/8" = 1'-0" | 1:96 | Commercial floor plans, building sections |
| 3/16" = 1'-0" | 1:64 | Floor plans that need a little more detail |
| 1/4" = 1'-0" | 1:48 | House floor plans, elevations (the most common) |
| 3/8" = 1'-0" | 1:32 | Enlarged plans |
| 1/2" = 1'-0" | 1:24 | Kitchen and bathroom plans, interior elevations |
| 3/4" = 1'-0" | 1:16 | Wall sections, cabinet details |
| 1" = 1'-0" | 1:12 | Details |
| 1 1/2" = 1'-0" | 1:8 | Construction details |
| 3" = 1'-0" | 1:4 | Large details, millwork |
Engineering and metric scales
Civil and site drawings use an engineer scale (1 inch = a number of feet). Metric drawings use a plain ratio.
| Engineer scale | Factor | Typical use |
|---|---|---|
| 1" = 10' | 1:120 | Site plans for a single lot |
| 1" = 20' | 1:240 | Site and grading plans |
| 1" = 30' | 1:360 | Larger sites |
| 1" = 40' | 1:480 | Subdivisions |
| 1" = 50' | 1:600 | Road and utility plans |
| 1" = 100' | 1:1200 | Master plans, maps |
| Metric scale | 1 cm on paper = | Typical use |
|---|---|---|
| 1:5 / 1:10 | 5 / 10 cm | Details |
| 1:20 | 20 cm | Room layouts, interior elevations |
| 1:50 | 50 cm | Floor plans, sections |
| 1:100 | 1 m | Floor plans, elevations |
| 1:200 | 2 m | Site plans, large buildings |
| 1:500 / 1:1250 | 5 m / 12.5 m | Site and location plans |
How to find the scale factor of any scale
- Architect scale (x" = 1'-0"): factor = 12 ÷ x. For 3/8" scale: 12 ÷ 0.375 = 32.
- Engineer scale (1" = y'): factor = y x 12. For 1" = 20': 20 x 12 = 240.
- Metric ratio (1:n): the factor is n.
- Unknown scale: measure a dimension that is written on the drawing (a dimension string), or an exterior entry door (usually 3'-0"), and divide the real size by the drawn size. Interior doors vary, so do not use them.
Printed PDFs are often resized to fit the paper. Check the graphic scale bar or a known dimension before you measure, because "fit to page" changes the scale.
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Frequently asked questions
What is the scale factor of 1/4 inch = 1 foot?
The scale factor is 48 (1:48). One foot is 12 inches, and 12 ÷ 0.25 = 48, so the drawing is 48 times smaller than the real building.
What is the scale factor of 1/8 inch = 1 foot?
It is 96 (1:96). A 40 ft wall at 1/8" scale is 480 ÷ 96 = 5 inches long on the drawing.
Is 1:50 the same as 1/4 inch scale?
Close, but no. 1/4" = 1'-0" is 1:48. Metric 1:50 is about 4% smaller. Do not measure a 1:50 drawing with an imperial 1/4" scale ruler.
What scale are house floor plans drawn at?
In the US, house floor plans are usually 1/4" = 1'-0" (1:48). Large houses or commercial buildings use 1/8" = 1'-0". Metric plans use 1:50 or 1:100.
How do I convert a real measurement to scale?
Convert the real measurement to inches, then divide by the scale factor. A 10 ft room at 1/2" scale is 120 ÷ 24 = 5 inches on the drawing.
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Sources: Scales follow standard US architect and engineer scale rulers, ISO 5455 metric scales and the UK 1:1250 location-plan scale.