Whether you’re building a scale model, reading a blueprint, or interpreting a map, knowing any two of scale ratio, real size, and model size lets you find the third. This calculator solves all three directions.

How to use this scale calculator

1. Choose your mode: Find Real Size, Find Model Size, or Find Scale Ratio.
2. Enter the Scale Ratio (e.g. 24 for a 1:24 scale) and either the Model or Real size, depending on your mode.
3. Read the calculated result.

What this calculator does

A scale ratio like 1:24 means 1 unit on the model equals 24 units in real life. Given any two of scale ratio, real size, and model/scaled size, this calculator finds the third, or works out the scale ratio directly between two known sizes.

Common scale ratios and where they come from

Certain scale ratios are conventional within specific hobbies and industries: 1:12 is standard for dollhouses, 1:24, 1:32, 1:48, and 1:64 are common die-cast and model vehicle scales, 1:87 (HO scale) is the most popular model railroad scale worldwide, and 1:144 and 1:285 appear in aircraft and military miniature modeling. These conventions exist so models, parts, and accessories from different manufacturers remain compatible within the same scale.

Why real and model size must use the same unit

Since the scale ratio is a pure ratio between two lengths, both the real size and model size need to be measured in the same unit (inches, centimeters, etc.) for the math to work correctly, this calculator handles that by applying your selected unit consistently to both values.

Frequently asked questions