Ratio Calculator
Scale a ratio up or down, or reduce it to its simplest form.
| A : B = C : D, so D = | 12 |
|---|---|
| Simplest form | 3 : 4 |
| As 1 : n | 1 : 1.333333 |
| As n : 1 | 0.75 : 1 |
How to use it
- Enter the ratio A:B.
- To scale it, enter C; the matching D is worked out. Leave C empty to just simplify.
- Useful for recipes, mixing ratios, maps and screen sizes.
Formula
A : B = C : D, so D = C × B ÷ A- Simplest form: divide A and B by their greatest common divisor (decimals are scaled to whole numbers first)
Example
3 : 4 = 9 : D gives D = 9 × 4 ÷ 3 = 12. The ratio 12 : 16 simplifies to 3 : 4, and 1.5 : 2.25 simplifies to 2 : 3.
Questions
How do I scale a recipe?
If a recipe for 4 uses 3 cups of flour and you're cooking for 6, solve 4 : 3 = 6 : D. D = 6 × 3 ÷ 4 = 4.5 cups.
Is a ratio the same as a fraction?
Close: the ratio 3 : 4 means the first part is 3/4 of the second, or 3/7 of the total.
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Last reviewed 2026-10-11. Found a mistake? Tell us.