One ratio, every scale
Scale modeling speaks in ratios: 1:24 cars, 1:50 site plans, 1:87 HO trains, 1:12 dollhouses. Enter the real-world dimension and the ratio — the model size is the real dimension ÷ the ratio — and the calculator does the division in the units you measured in.
Sources and standards
Where these figures come from
Every formula on this page is implemented from the published reference material below. Where a value depends on a regional code, the calculator lets you override it rather than assuming one jurisdiction.
- NIST Office of Weights and Measures — the US customary and SI conversion factors used throughout this tool.
- International Code Council — the International Residential Code and International Building Code.
Figures, formulas and reference tables last verified: 19 September 2026.