Model Train Scale Converter
Convert real-world dimensions to any model railway scale — and back — across HO, N, O, G and more.
How it works
Model length = real length ÷ scale ratio · Real length = model length × scale ratio
Every model railway scale is a fixed ratio between model and prototype — HO is 1:87, meaning 87 model units equal one real unit. Scaling down divides by that ratio; scaling up multiplies by it. Because the ratio is dimensionless, you can work in any unit as long as input and output match, so this converter normalises everything to metres internally and reports the result in several units.
Worked example
A 20 m real coach in HO (1:87) becomes 20 ÷ 87 ≈ 0.23 m, or about 230 mm long. Going the other way, a 230 mm HO model represents 230 × 87 ≈ 20 m in the real world.
Frequently asked questions
What is the most common model train scale?
HO (1:87) is the most popular worldwide, prized for balancing detail against layout space. N scale (1:160) is roughly half the size and popular where space is tight; O scale (1:48) is much larger and favoured for detail and garden lines.
What is the difference between scale and gauge?
Scale is the size ratio of the whole model; gauge is only the distance between the rails. Two models at the same scale can run on different gauges, and standardized gauge names (like HO or N) usually imply a scale but are not identical to it.
Can I convert between two model scales?
Yes — scale up from the first scale to real size, then scale down into the second. For example an N-scale (1:160) building is 160 ÷ 87 ≈ 1.84 times smaller than the HO version of the same prototype.
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This calculator is for educational purposes. Double-check important results before acting on them.