Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Scale size (in)
5.511
Scale size (mm)
139.98
Scale size (ft)
0.459
Scale ratio (1:X)
87.1
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter prototype dimension (in).
- 2Enter scale.
- 3Read your scale size (in) on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
HO, N, O, 1:72, 1:35 — enter a prototype dimension and get the scale size in inches and millimeters.
Worked example
Using the values the calculator loads with:
Inputs
- Prototype dimension: 480 in
- Scale: HO (1:87)
Results
- Scale size (in): 5.511
- Scale size (mm): 139.98
- Scale size (ft): 0.459
- Scale ratio (1:X): 87.1
What each field means
Inputs
- Prototype dimension (in)
- The prototype dimension used in the calculation, measured in in. Starts at 480 in so you have a working example on load.
- Scale
- Pick the option that matches your situation — the maths changes per option. Choices: N (1:160), HO (1:87), OO (1:76), 1:72, O (1:48), 1:35, G (1:24).
Results
- Scale size (in)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Scale size (mm)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Scale size (ft)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Scale ratio (1:X)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the model scale conversion calculator work?
HO, N, O, 1:72, 1:35 — enter a prototype dimension and get the scale size in inches and millimeters.
What do I need to enter?
2 values: prototype dimension, and scale. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the scale size (in) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Model Scale Conversion Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/model-railroad-scale
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/model-railroad-scale" target="_blank" rel="noopener">Model Scale Conversion Calculator — RevenueLab</a> (2026).</p>
Source: [Model Scale Conversion Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/model-railroad-scale) (2026).