Convert a measured drawing dimension to its real-world size. Or work back the other way. At any scale ratio 1:N.
Lengths scale by N; areas scale by N² (the square of the linear ratio). Pick a standard scale or type your own.
For design guidance only. Always verify against the originating drawing and its stated scale.
About this drawing scale converter
This free drawing scale converter turns a dimension measured off a scaled drawing into its real-world size, or works the conversion back the other way. Enter the scale ratio as 1:N, choose whether you are converting a length or an area, type the measured value and pick its unit. It returns the converted value in the same unit and tidily expressed in metres. It is aimed at UK estimators, contractors and surveyors taking off quantities from architects' and engineers' drawings at tender stage. Standard scales are offered as one-tap presets, but any denominator works.
How drawing scales are calculated
A scale of 1:N means one unit on the drawing represents N units in reality. For a length, the real size is measured × N and the drawing size is measured ÷ N. For an area the factor is N², not N, because area scales as the square of the linear ratio, a 1:100 plan shrinks every length 100× but every area 10,000×. The recommended scales (1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100, 1:200, 1:500, 1:1000, 1:2000, 1:5000 and their decimal multiples) come from ISO 5455 / BS EN ISO 5455 "Technical drawings. Scales"; UK construction practice adds 1:1250 and 1:2500, the Ordnance Survey location-plan scales.
Frequently asked questions
What does a scale of 1:50 mean?
One unit measured on the drawing equals 50 units in reality. So 27 mm on a 1:50 drawing is 27 × 50 = 1350 mm, i.e. 1.35 m on site.
Why do areas use N² instead of N?
Area is length × length, so both dimensions scale by N and the area scales by N × N. At 1:100 a length is 100× larger in reality but an area is 100² = 10,000× larger. Switch the type to "Area" and the converter applies N² automatically.
Which scales are standard for UK drawings?
ISO 5455 sets the recommended series (1:1 up to 1:5000 and their decimal multiples). RIBA practice also uses 1:1250 and 1:2500 for Ordnance Survey location plans. All of these are one-tap presets, and you can type any other denominator.