What a drawing scale really is
Every drawing scale is a ratio between a length on paper and the real length it stands for. Engineering scales write it as 1 inch to some feet, architectural scales as a fraction of an inch to a foot, and metric drawings as a plain ratio. Converting them all to the same form, real length divided by paper length in the same units, is what makes them comparable: 1" = 20' is 1:240, 1/8" = 1'-0" is 1:96, and 1:250 is close to, but not the same as, 1" = 20'.
How to use the drawing scale converter
Look up a scale
Choose the scale printed on the sheet, or type a custom ratio. The converter shows the ratio, what one inch on paper represents, how much paper one foot takes, and the metric equivalent of a millimeter.
Paper to real, and back
Type a length measured off the paper with a ruler and read the real length, in feet, feet and inches, or meters. Or type the real length and get how long it should be on paper, which is handy for checking a print.
Reprint at another scale
Pick a new scale to see the percentage to print or copy at. Going from 1" = 20' to 1" = 40' is 50%; going from 1:500 to 1:200 is 250%.
The true scale of a resized sheet
This is where most measurement mistakes come from. A sheet drawn on ARCH D (24 x 36) and printed on 11 x 17 with fit to page shrinks to fit the tighter edge, which is 11 / 24, about 45.8%. A 1" = 20' plan now reads about 1" = 43.6', yet the title block still says 1" = 20'. Pick the original and printed sheet sizes and the converter gives the scale the print actually has. Printer margins can shrink it a little further, so measure a printed dimension to confirm.
Common conversions
- 1" = 10' is 1:120. 1" = 20' is 1:240. 1" = 50' is 1:600. 1" = 100' is 1:1200.
- 1/8" = 1'-0" is 1:96. 1/4" = 1'-0" is 1:48. 1/2" = 1'-0" is 1:24.
- A half-size print doubles the ratio: 1" = 20' becomes 1" = 40'.
- Metric ratios work in any unit: at 1:100, 1 mm on paper is 100 mm, or 0.1 m, on site.
Scales and the free tools
Once you know the scale, the measure tool uses it on the drawing itself: pick the same scale, or calibrate from a printed dimension when the sheet has been resized, and click from point to point for real-world lengths. The area calculator does the same for square feet and acres.