Scale calculator
This scale calculator converts measurements between a drawing and the real world and resizes them from one scale to another. Pick the real size, drawing size, scale itself, or the new size after changing scale.
It suits architectural plans, maps, dioramas and scale models alike.
Result
12 m
1,200 cm · 0.012 km
A 1:100 scale means 1 cm on the drawing equals 100 cm in reality.
How scale works
A 1:100 scale means one centimetre on the drawing represents one hundred centimetres — one metre — in reality. The first number is the drawing, the second is the real object.
- Real size = drawing size × scale denominator.
- Drawing size = real size ÷ scale denominator.
- Scale = real size ÷ drawing size.
- Size at new scale = original size × original denominator ÷ new denominator.
- Example: 12 cm at 1:100 equals 12 m in reality.
How to convert a size from one scale to another
To resize a drawing or model, multiply its original size by the original scale denominator and divide by the new denominator. The measurement unit stays the same.
For example, a 10 cm part at 1:42 becomes 10 × 42 ÷ 60 = 7 cm at 1:60. Moving from 1:100 to 1:50 doubles the drawing size instead.
Architectural drawing scales
| Scale | 1 cm on paper | Typical use |
|---|---|---|
| 1:20 | 20 cm | details and joints |
| 1:50 | 50 cm | single room plans |
| 1:100 | 1 m | floor plans |
| 1:200 | 2 m | whole building plans |
| 1:500 | 5 m | site plans |
Map scales
| Scale | 1 cm on the map | Map type |
|---|---|---|
| 1:10,000 | 100 m | city plan |
| 1:25,000 | 250 m | hiking map |
| 1:100,000 | 1 km | regional map |
| 1:500,000 | 5 km | state map |
| 1:1,000,000 | 10 km | overview map |
Model scales
- 1:87 (HO) is the most common model railway scale.
- 1:43 is the classic collectible car scale.
- 1:72 and 1:48 are standard for aircraft kits.
- 1:35 is the usual armour modelling scale.
Frequently asked questions
What does a 1:100 scale mean?
One centimetre on the drawing equals one hundred centimetres, that is one metre, in reality.
How do I convert a drawing measurement to real size?
Multiply the drawing measurement by the scale denominator. 8 cm at 1:50 equals 4 metres.
How do I find the scale of a drawing?
Divide the real size by the size on the drawing. If 3 m appears as 6 cm, the scale is 1:50.
How do I convert a drawing from 1:50 to 1:100?
Multiply each size by 50 and divide by 100. The new drawing is half as large: 10 cm at 1:50 becomes 5 cm at 1:100.
How far is 1 cm on a 1:25,000 map?
250 metres on the ground.
What is the difference between reduction and enlargement scales?
Reductions start with one, such as 1:100. Enlargements end with one: 2:1 means the drawing is twice the real size.
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Updated: 2026-08-09