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Model Railway Scale Converter

Pick a scale, then turn a real length into the size of the model, a model length into real life, or move a dimension from one scale to another: HO to N, OO to HO, any 1:n ratio.

Model size

100 mm

10 cm · 1000 × 8.71 m ÷ 87.1

A scale is a size ratio, not a track gauge. Ratios follow the NMRA list; if your manufacturer states another ratio, choose “Other”.

How it works

  1. Choose what to convert: real to model, model to real, or one scale to another.
  2. Pick the scale from the list, or choose “Other” and type the ratio (87.1 for 1:87.1).
  3. Enter the length and read the result with its formula.
  4. Copy the result to paste it into your plan or your notes.

What people use it for

  • Sizing a building or a wagon

    A real 8.71 m wall is 100 mm in HO: check a kit or a scratch-build against the real thing.

  • Reusing a plan

    Move a drawing from HO to N, or from OO to HO, without redoing the measurements.

  • Checking a model

    Find the real length that a model wagon or platform stands for.

Questions

Which ratios does it offer?
The common proportions listed by the NMRA: Z 1:220, N 1:160, TT 1:120, HO 1:87.1, OO 1:76.2, S 1:64 and O 1:48. For anything else, choose “Other” and type the ratio: 148 for 1:148, for example.
What are the formulas?
Model (mm) = 1000 × real length (m) ÷ n. Real (m) = model (mm) × n ÷ 1000. Between scales 1:a and 1:b: dimension × a ÷ b. The results are rounded for display only.
Is a scale the same as a gauge?
No. The scale is the size ratio of the model; the gauge is the distance between the rails. The same scale can run on several gauges (narrow-gauge models, for example), so a length converted here says nothing about track.
Why do some HO and OO figures differ?
Regions use slightly different ratios for the same name (OO is 1:76.2 on the NMRA list, and ratios such as 1:87 are also used for HO). If your manufacturer states another ratio, type it as “Other”.