How do I measure real-world dimensions for my model?

Use published drawings, manufacturer specifications, or reference books. For aircraft, wingspan and fuselage length are commonly available. For buildings, measure or estimate from maps. Many online resources provide three-view drawings with dimensions.

Why does my model not match the calculated size exactly?

Kit manufacturers sometimes make small compromises for moulding reasons or to fit standard box sizes. Check the kit instructions for any noted deviations. Also, real vehicles and aircraft often varied slightly between production batches.

Can I enter measurements in mixed units?

Yes — enter metres, centimetres and millimetres separately and they will be combined. For example, a 12.5m measurement can be entered as 12m and 500mm, or 12m and 50cm, whichever is most convenient.

ModelCalcs.uk

Real to Scale Converter — Shrink Real Dimensions

Enter a real-world measurement in metres, centimetres and millimetres and see the exact model-scale equivalent.

Metres

Whole metres of the real prototype (e.g. 20 for a 20.5 m loco)

Centimetres

Extra centimetres on top of the metres above

Millimetres

Extra millimetres for fine prototype dimensions

ScaleYour model's scale (OO = 1:76.2, HO = 1:87.1, N UK = 1:148). Pick Custom for any other ratio.

How We Calculate This

This calculator combines your metre, centimetre and millimetre inputs into a total real-world measurement in millimetres, then divides by the scale factor to give the model dimension.

Formula

Model size (mm) = Total real size (mm) ÷ Scale factor

Example: A real locomotive 20.5 m long at OO gauge (1:76.2):
20,500 mm ÷ 76.2 = 269.0 mm (about 27 cm) on the model.

We use the exact modelling ratios: OO is precisely 1:76.2 (4 mm to the foot) and HO is 1:87.1 (3.5 mm to the foot), not the rounded 1:76 / 1:87 sometimes quoted. British N gauge is 1:148 (not the continental/US 1:160) because early motors would not fit smaller British loco bodies.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.