Scale Calculator
A scale converter turns the shrunk-down measurements on a map, plan or model into real-world distances, and back again, so you never have to guess what a drawing actually represents. Every scaled drawing carries a ratio written as 1:N, meaning that one unit on the page stands for N of the same units in real life. At 1:100, one centimetre on the plan is one hundred centimetres, or one metre, in the building it describes. This calculator works in both directions. Give it a real length and it returns the scale length you should draw or measure on the model, by dividing the real length by N. Give it a scale length and it returns the real length the object truly is, by multiplying by N. You choose the unit you prefer, from millimetres and centimetres through metres and kilometres to inches and feet, and the calculator keeps both lengths in that same unit so the answer reads cleanly without any mental conversion. Because the ratio itself carries no units, the same scale holds true whatever measurement system you work in, which makes it just as useful for an architect setting out floor plans, a model railway builder checking carriage lengths, a hobbyist printing a scaled template, a student answering a geometry question, or a tramper reading distances off a topographic map. The plain-language summary spells the relationship out in words as well as numbers, so there is no ambiguity about which way the conversion has gone. Enter your scale ratio and a length below, pick what you want to solve for, and the result updates instantly as you type.
The formula
A scale of 1:N means one unit on the drawing represents N units in real life. To find the scale length, divide the real length by N. To find the real length, multiply the scale length by N. Both lengths must be in the same unit, and this calculator keeps them in the unit you select.
scale length = real length / N
real length = scale length × N
Worked example
An object is 5 metres long and you are drawing it at a scale of 1:100. The scale length is 5 / 100 = 0.05 metres, which is 5 centimetres on the page. Reversing it, a 0.05 metre line on a 1:100 plan represents 0.05 × 100 = 5 metres in real life.
Who this calculator is for
This calculator is for architects, draughters, model makers, hobbyists, students and map readers who need to convert between real distances and the scaled lengths shown on a drawing, plan, model or map.
What this calculator assumes
- The scale is expressed as a ratio 1:N, where one drawing unit represents N real units.
- The real length and the scale length are entered in the same unit, which you select.
- Scale length equals real length divided by N; real length equals scale length multiplied by N.
- Results are rounded for display.
Frequently asked questions
What does a scale of 1:N mean?
One unit on the drawing or model represents N of the same units in real life. At 1:100, one centimetre on the plan represents 100 centimetres, or one metre.
How do I convert a real length to a scale length?
Divide the real length by N. At 1:100, a real length of 5 metres becomes 5 / 100 = 0.05 metres, or 5 centimetres on the drawing.
How do I convert a scale length back to a real length?
Multiply the scale length by N. At 1:100, a 0.05 metre drawing length represents 0.05 × 100 = 5 metres.
Does the unit matter in a scale ratio?
The ratio is unitless, so 1:100 holds whatever unit you choose, as long as both lengths use the same unit.
Related calculators
- Perimeter Calculator: distance around a shape.
- Probability Calculator: the chance of an event.
- Standard Deviation Calculator: spread of a data set.
- All Maths & Statistics Calculators.