Setting out
Drawing scale
- where
- real length (mm)
- drawing length (mm)
- scale denominator (1:n)
Explain this equation
This converts a length measured on a drawing into a real length at a 1:n scale, and the other way round. Use it when a dimension is missing and you have to scale it off a print.
D is the length on the drawing in mm. n is the scale denominator, so 1:50 means n = 50. R is the real length in mm. The calculator also gives R in metres.
At 1:n, one millimetre on paper stands for n millimetres in reality, so the real length is D × n. Working backwards, the drawing length is R / n. The real length in metres is just R divided by 1000.
At 1:50, 40 mm on the drawing is 2000 mm, or 2 m, on site. At 1:100 the same 40 mm would be 4 m.
Watch out: always prefer a written dimension. Prints that have been resized, or measured on a zoomed screen, are no longer at the stated scale.
Convert a measured drawing length at a stated 1:n scale.
Enter your values to see the result.
Good to know
Prefer written dimensions. Check the print calibration; screen zoom and resized prints change the effective scale.
Sources
- Geometry / arithmetic
Estimates are not design approval or British Standards compliance checks. Structural arch, retaining-wall, wind, foundation, lintel and masonry-capacity design are not performed. Use the project engineer’s specification.