How to convert measurements at a 1:n scale
Use this scale calculator to interpret dimensions on architectural drawings, maps, sketches and models. Convert drawing distances to real distances and back at 1:20, 1:50, 1:100, 1:50,000 or a custom scale. You can also find the scale from two known lengths and calculate the photocopy percentage required to change from one scale to another. Units are converted before applying the formulas. Printing a document to fit a page may invalidate the printed scale.
Example: on a 1:50,000 map, 3 cm corresponds to 3 × 50,000 cm = 150,000 cm = 1.5 km on the ground. To change a 1:100 drawing to 1:50, print at 200%.
Results are estimates and depend on the supplied values.
How to use scales for buildings, maps and models
What does 1:50 or 1:100 mean?
A 1:50 drawing represents 50 real units for each drawn unit. At 1:100, one unit on the drawing equals 100 real units, so 1 cm on a 1:100 plan represents 1 m in reality.
Real-world distance = drawing distance × n
How to convert a real length to a drawing
First convert lengths into matching units and divide the real length by the scale denominator. A 5 m wall is drawn as 5 cm at 1:100.
Drawing distance = real-world distance ÷ n
How to find an unknown scale
If you know the true physical distance and the length measured on paper, express both in the same unit and divide reality by drawing. A 4 m wall shown as 8 cm implies 1:50.
n = real length (matching unit) ÷ drawing length
How to resize a drawing between scales
To print or photocopy from one scale to another, divide the old denominator by the new one and multiply by 100. From 1:100 to 1:50 requires 200%; the reverse requires 50%.
Print percentage = original denominator ÷ target denominator × 100
Why area does not scale like length
If lengths change by a factor of n, areas change by n² and volumes by n³. The calculator shows n² to avoid applying a linear factor incorrectly to an area.
Area scale factor = n² · Volume scale factor = n³
Practical cautionsThe 1:n ratio is reliable only when the drawing is reproduced at its intended physical size. PDF zoom, fit-to-page printing, resized images and map distortion can change the apparent scale. Check against a known length before making construction or surveying decisions.
Basis and referencesGeometric ratio formulas. The US Forest Service explains that at 1:24,000 map scale, one drawn unit equals 24,000 units on the ground; unit conversions use exact international factors.
US Forest Service — Map scale reference
Frequently asked questions
How many centimetres represent 1 metre at 1:100?
It is 1 cm on the drawing because 1 m is 100 cm and 100 ÷ 100 = 1.
How long is 1 metre at 1:50?
It corresponds to 2 cm on the drawing. A 1:50 scale divides actual lengths by 50.
How do I convert centimetres on a 1:50,000 map to kilometres?
Multiply the map centimetres by 50,000, then divide by 100,000 to obtain kilometres. For example, 3 cm equals 1.5 km.
What print percentage changes 1:100 to 1:50?
Print at 200%. To go from 1:50 to 1:100, print at 50%.
Can I find the scale from two known distances?
Yes. Enter the drawing and actual distances; the calculator converts the units and divides the real length by the drawing length.
Why is a measurement on screen different from the stated scale?
Zoom, screen resolution and fit-to-page printing do not necessarily preserve the drawing’s original physical dimensions.