About us

A free tool for anyone working with scales: model railway fans, die-cast collectors, kit builders, architects and hikers reading maps. It’s built to give a clear answer quickly, on any device, without sign-ups or adverts.

Open the converter

Guide

How the maths works

A scale of 1:N means one unit on the model stands for N of the same unit in real life. At 1:87, 1 mm on the model is 87 mm on the real thing. Every calculator on the site uses one of these rules:

Model size

model = real ÷ N

A 4.5 m car at 1:24 is 4.5 ÷ 24 = 18.75 cm.

Real size

real = model × N

A 20 mm figure at 1:87 is 20 × 87 = 1.74 m.

The scale

N = real ÷ model

A 1.8 m person modelled at 20.7 mm is about 1:87 (HO).

Change scale

new = old × N₁ ÷ N₂

100 mm at 1:72 becomes 150 mm at 1:48 (print at 150%).

Map distance

ground = map × N

4 cm on a 1:25,000 map is 4 × 25,000 = 1 km.

Areas and volumes

Areas scale by the square of the scale number and volumes by its cube. At 1:100, a 20 m² room is 20 ÷ 100² = 20 cm² on the plan, and 1 m³ at 1:10 is 1 ÷ 10³ = 1 litre.

Walking and hiking time

Walking time assumes 5 km/h. Hiking time uses Naismith’s rule: 5 km/h, plus an hour for every 600 m of climb.

The converter handles units for you, including feet and inches, and rounds answers to 4 significant figures (2 decimal places below 1 mm). Open “Show in other units” for every unit at once.

Accuracy

How we check the numbers

Every answer comes from the formulas above, worked out in your browser. An automated test suite checks the calculators against worked examples, such as a 1.8 m person at HO being 20.69 mm and 4 cm on a 1:25,000 map being 1 km, so a change to the site cannot quietly break the maths.

Ratios are exact by definition. Track gauges and map series come from these published standards:

MOROP NEM 010: European model railway scales and track gauges (Z, N, TT, H0, 0, 1, G).
NMRA Standards: North American model railway scales and gauges (N, HO, S, O).
Ordnance Survey: UK map scales (1:25,000 Explorer, 1:50,000 Landranger).
U.S. Geological Survey: US topographic map scales (1:24,000 7.5-minute series).

Figures last checked: 19 October 2026.

Privacy

Your numbers never leave your device

Nothing is sent anywhere. Every calculation runs in your browser.
Your browser remembers a few settings so the page opens where you left off: your last calculation, recent calculations, light or dark theme, metric or imperial, fraction rounding, paper size and 3D printer size. Clear them any time from your browser’s site data, or with “Clear history”.
No accounts, no cookies, no adverts and no tracking.
Fonts are served from this site, so no third party sees your visit. If you install the site as an app, its pages are saved on your device so they work offline.

Read the full privacy policy.

Feedback

Get in touch

Found a mistake, or missing a scale you use? Contact us.

For clubs and blogs

Add the converter to your site

Paste this code into any page, such as a club website or a modelling blog, to show the full converter there. It is free to use; please keep the credit link.

<iframe src="https://onlinescaleconverter.com/embed" title="Scale converter" width="100%" height="1250" style="border:0;max-width:960px" loading="lazy"></iframe>
<p><a href="https://onlinescaleconverter.com/">Scale converter</a> for models, plans and maps</p>

Changelog

What’s new

Version 2.1 19 October 2026
- Convert several sizes at once: type length × width × height, like 120 x 60 x 75.
- Answers in feet, inches and fractions, rounded to the nearest 1/16″, 1/32″ or 1/64″.
- “Will it fit on paper?” checks a drawing against A4 to A0, Letter, Tabloid or ARCH D and suggests a scale that fits.
- Change scale shows the slicer percentage, with its own copy button.
- Map answers give inches to the mile, and the ruler prints as a scale bar.
- The size-comparison drawing and the separate pages for each scale were retired.
Version 2.0 18 October 2026
- A new look: clearer layout, light and dark themes, and an answer you can read at a glance.
- Search the scale list by name or number, or type any scale, including “1 inch to the mile”.
- A drawing compares the real object with the model at true size.
- Areas and volumes, a list converter, a printable scale ruler and a 3D-printer size check.
- Hiking time for map routes using Naismith’s rule.
- Recent calculations, keyboard shortcuts, and offline use once installed.
- Pages for more scales, including 1:48, 1:87 and 1:100.
Version 1.0 18 October 2026
- Five calculators: model size, real size, the scale, change scale and map distance.
- Scale charts and worked examples.