Scale converter

Choose the scale above and a scale bar for it appears below the result: black and white divisions of a round real length, such as 5 m at 1:50 or 10 ft at 1/4" = 1'-0", about 5 to 12.5 cm long on paper. Download it as an SVG to place in the drawing, or as a PDF to print. Because the bar grows and shrinks with the drawing, it still measures correctly after the plan has been printed at another size.

Measure the distance on the drawing and multiply by the scale number. At 1:50, 24 mm on the plan is 24 × 50 = 1,200 mm, or 1.2 m. For US architectural scales, divide the scale into the foot first: 1/4" = 1'-0" means every quarter inch is a foot, which is a ratio of 1:48, so 2 inches on the plan is 2 × 48 = 96 inches, or 8 feet. The converter above does both directions and shows metric and feet-and-inches together.

One unit on the paper stands for fifty of the same unit in reality: 1 mm for 50 mm, 1 cm for half a metre. It is unit-free, which is why metric drawings use it. 1:50 and 1:100 are the usual scales for building plans, 1:20 and 1:10 for details, 1:200 to 1:1250 for site and location plans.

1:48. A foot is 12 inches, and 12 divided by 1/4 is 48. The same rule gives 1/8" = 1'-0" as 1:96, 1/2" = 1'-0" as 1:24 and 3/16" = 1'-0" as 1:64. Engineering scales work the same way: 1" = 20' is 1:240, because 20 feet is 240 inches.

Measure something on the drawing whose real size you know — a door (usually about 800–900 mm or 30–36 in wide), a dimensioned wall, a scale bar — and enter both lengths under Find the scale. The ratio of real to drawing is the scale. If the answer is close to a standard scale but not on it, the drawing has probably been printed or copied at the wrong size: a 1:50 plan copied at 71% measures as about 1:70.

Only if it prints at exactly 100%. Most print dialogs shrink the page by 3–6% to fit the printer’s margins, and every measurement taken from that print is off by the same amount. Print at Actual size, and check with the print scale calibration test before trusting a printed plan.