Model scale calculator
Convert sizes between the original and the model at a 1:N scale.
Fill in the fields and the result will appear here automatically.
Converts three ways: what the model size will be, what the original measured, and what scale an existing pair of sizes represents. The scale denominator is a first-class input in a modeller's own vocabulary — 1:87, 1:43, 1:72 — not an anonymous term of a proportion you have to arrange yourself. Answers come in millimetres, and a scale you look up is printed the familiar way, as 1:N.
How it works
Formula and logic
Model = original ÷ denominator; original = model × denominator; scale = original ÷ model. Only the two known quantities are entered; the unknown field is hidden and ignored. Lengths in mm must be positive and N>0. N>1 reduces the model and 0<N<1 enlarges it. This is a linear scale; displayed rounding does not set a manufacturing tolerance.
Example
A 4350 mm wagon at 1:87 gives a 50 mm model.
Fields and units
- What to find — list option
- Real size, mm — mm
- Model size, mm — mm
- Scale denominator, 1:N — unitless
How to use
- — Choose what to find: the model size, the real size, or the scale itself.
- — Enter sizes in millimetres — that is how drawings are marked and models are measured.
- — The scale denominator is the second number of the notation: for 1:87 it is 87.
- — Only the two known quantities are entered; the unknown field is hidden and ignored.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- This is a linear scale; displayed rounding does not set a manufacturing tolerance.
FAQ
What does the second number in 1:87 mean?
N is the original length divided by model length. At 1:87 one model millimetre corresponds to 87mm of the original;0<N<1 produces an enlargement.
How is this different from a proportion calculator?
A proportion solves an anonymous a : b = c : d and leaves you to place the denominator. Here the scale is its own field, answers carry millimetres, and a scale you look up prints as 1:N.
The scale came out fractional — is that wrong?
No. An arbitrary pair of sizes rarely lands on a round number: 1:12.5 simply means the original is 12.5 times larger. For standard rulers pick the nearest accepted scale.
Does it work for areas and volumes?
The fields handle linear sizes. Area shrinks by N² and volume by N³, so square metres must not be entered here.