Ratio Calculator
Recipes, paint mixes, model scales: whenever two amounts have to stay in step, this page keeps them there. Solve for a missing value, boil a ratio down, or scale one up. The answer follows your typing.
Three numbers in, one blank left for me.
Decimals welcome; 1.5 : 2.5 turns into 3 : 5.
Doubling a recipe is just multiplying by 2.
Ratios in Plain Terms
A ratio like 2:3 says "for every 2 of the first thing, 3 of the second." Two ratios describe the same relationship when their cross products match: a:b equals c:d exactly when a × d = b × c. That one fact powers the solver above; multiply crosswise, divide by what's left, done.
Simplifying and scaling
To simplify, divide both sides by the biggest number that goes into both. 8:12 becomes 2:3 because 4 divides into each. Scaling goes the other way, multiplying both sides by the same amount, and the relationship never changes:
| Ratio | Same as |
|---|---|
| 2 : 3 | the simplest form |
| 4 : 6 | 2 : 3 doubled |
| 8 : 12 | 2 : 3 times four |
| 10 : 15 | 2 : 3 times five |
A ratio a:b behaves a lot like the fraction a/b, so if your problem is written with numerators and denominators, the fraction calculator speaks that dialect. And when one side of your comparison is "out of 100", you're really asking a percent question; the percentage calculator handles those directly.