What does 1:20 scale mean?

At 1:20, one unit on the drawing is 20 of the same unit in real life. 1 mm on paper is 20 mm (0.02 m) in reality, and 1 cm on paper is 0.2 m.

How do I convert 1:20 to real size?

Multiply the measurement on paper by 20. A 25 mm line on a 1:20 drawing is 500 mm, or 0.5 m.

How do I check a drawing is really at 1:20?

Measure a printed dimension on the sheet and divide the real length by the paper length. If you don't get 20, the sheet was printed or exported at a different size and the scale note no longer applies. Set the scale from the dimension instead.

Drawing scales

1:20 scale

1:20 is a 1:20 scale. A metric scale used for details and enlarged plans. Conversion tables both ways.

Updated October 12, 2026 · FloorFigures

Short answer

1:20 means every millimeter on the drawing is 20 mm in real life. 1 cm on paper is 0.2 m. A metric scale used for details and enlarged plans.

1:20 conversion: paper to real size

On paper	Real size
1 mm	0.02 m
5 mm	0.1 m
10 mm	0.2 m
20 mm	0.4 m
50 mm	1 m
100 mm	2 m
200 mm	4 m

Real size to paper at 1:20

Real size	On paper
0.9 m	45 mm
1 m	50 mm
3 m	150 mm
5 m	250 mm
10 m	500 mm
20 m	1,000 mm
50 m	2,500 mm

How much fits on a sheet

The largest area a full sheet can show at 1:20, before margins and title block:

Sheet	Paper size	Real area shown
A1	841 × 594 mm	16.8 × 11.9 m
A3	420 × 297 mm	8.4 × 5.9 m
A4	297 × 210 mm	5.9 × 4.2 m

Is your plan really at 1:20?

A scale note is only true at the paper size the drawing was made for. Print a 24" × 36" plan on letter paper with "fit to page", or export a PDF at a different page size, and every measurement shrinks by the same factor while the note still says 1:20. Always check one printed dimension before you trust the scale.

FloorFigures does this for you on PDFs: it reads the printed dimensions, works out the real scale, and warns you when the note disagrees. It's free and runs in your browser.

Other metric scales

Scale	Ratio	Typical use
1:50	1:50	A metric scale used for detailed floor plans and room layouts.
1:100	1:100	The standard metric scale for house floor plans, sections and elevations.
1:200	1:200	A metric scale used for plans of large buildings and small site plans.
1:500	1:500	A metric scale used for site and location plans.

Questions

What does 1:20 scale mean?: At 1:20, one unit on the drawing is 20 of the same unit in real life. 1 mm on paper is 20 mm (0.02 m) in reality, and 1 cm on paper is 0.2 m.
How do I convert 1:20 to real size?: Multiply the measurement on paper by 20. A 25 mm line on a 1:20 drawing is 500 mm, or 0.5 m.
What is 1:20 used for?: A metric scale used for details and enlarged plans.
How do I check a drawing is really at 1:20?: Measure a printed dimension on the sheet and divide the real length by the paper length. If you don't get 20, the sheet was printed or exported at a different size and the scale note no longer applies. Set the scale from the dimension instead.