An architectural scale states how much smaller the drawing is than the real building. Metric drawings write it as a ratio, such as 1:100 (1 unit on paper equals 100 units in reality). US imperial drawings write it as an equation, such as 1/4" = 1'-0" (a quarter inch on paper equals one foot), which is the same as 1:48. The scale only holds when the sheet is printed at its intended paper size; a PDF printed "fit to page" or viewed on screen is no longer at scale.
Common metric architectural scales
| Scale | 1 mm on paper equals | Typical use |
|---|---|---|
| 1:1250 / 1:1000 | 1.25 m / 1 m | Location plans, master plans |
| 1:500 | 0.5 m | Site plans for larger sites |
| 1:200 | 200 mm | Site plans, small-scale general arrangement plans |
| 1:100 | 100 mm | Floor plans, sections, elevations |
| 1:50 | 50 mm | Detailed plans and sections, room layouts |
| 1:20 | 20 mm | Part plans, wall sections, stairs |
| 1:10 / 1:5 | 10 mm / 5 mm | Construction details |
| 1:2 / 1:1 | 2 mm / 1 mm | Joinery and full-size details |
Common imperial architectural scales and their ratios
| Architectural scale | Ratio | Typical use |
|---|---|---|
| 1/16" = 1'-0" | 1:192 | Large floor plans, site plans |
| 3/32" = 1'-0" | 1:128 | Large plans |
| 1/8" = 1'-0" | 1:96 | Floor plans, elevations of larger buildings |
| 3/16" = 1'-0" | 1:64 | Floor plans |
| 1/4" = 1'-0" | 1:48 | Floor plans, elevations, sections of houses and smaller buildings |
| 3/8" = 1'-0" | 1:32 | Enlarged plans |
| 1/2" = 1'-0" | 1:24 | Enlarged plans, interior elevations |
| 3/4" = 1'-0" | 1:16 | Wall sections, details |
| 1" = 1'-0" | 1:12 | Details |
| 1 1/2" = 1'-0" | 1:8 | Details |
| 3" = 1'-0" | 1:4 | Large details |
Engineering (civil) scales work differently: 1" = 10', 1" = 20', 1" = 50' and so on, which are ratios of 1:120, 1:240 and 1:600.
How to convert an imperial scale to a ratio
Divide 12 by the inch fraction. For 1/4" = 1'-0": 12 ÷ 0.25 = 48, so the ratio is 1:48. For 3/16" = 1'-0": 12 ÷ 0.1875 = 64, so 1:64. For engineering scales, multiply the feet by 12: 1" = 20' is 1:240. Our drawing scale calculator does this both ways.
Why a PDF can be at the wrong scale
- Printed with "fit to page". The printer shrinks the sheet to fit the margins, so 1:100 becomes roughly 1:103. Print at 100% or "actual size". See printing drawings to scale.
- Printed on a different paper size. An A1 sheet at 1:100 printed on A3 becomes 1:200. Many title blocks say "1:100 @ A1" for exactly this reason. See drawing sheet sizes.
- A scanned drawing. Scanning and rescaling rarely preserves the exact size.
- Several scales on one sheet. A plan at 1:100 and details at 1:10 share a sheet; the scale in the title block may say "as noted".
Measuring a scaled PDF drawing on screen
On screen you do not need a scale ruler: a PDF measurement tool converts what you click into real dimensions. In Ncored, the PDF editor we built in our architecture studio, you choose the sheet's scale (1:50, 1:100 or any ratio you type, including 1:48 for a 1/4" drawing) or calibrate by clicking both ends of a dimension you know, then measure lengths, polylines and areas with snapping to the drawing's own lines. Results are in millimetres, centimetres or metres; feet and inches are not supported yet. It runs on Windows and Mac. More in the PDF measurement tool guide.
Frequently asked questions
What scale are architectural floor plans usually drawn at?
Metric floor plans are usually 1:100 or 1:50. US floor plans are usually 1/4" = 1'-0" (1:48) for smaller buildings or 1/8" = 1'-0" (1:96) for larger ones.
What does 1:100 mean on a drawing?
One unit on the drawing equals 100 of the same units in reality: 1 cm on paper is 1 m in the building.
What is 1/4 inch scale as a ratio?
1/4" = 1'-0" is 1:48.
What does "NTS" mean on a drawing?
Not to scale: the drawing is diagrammatic and must not be measured.
Related: how to read construction drawings, architectural title block guide, measure on a PDF drawing.