Ratio Calculator
Simplify ratios to lowest terms or solve a proportion for the missing value.
Simplifying works best with whole numbers. Proportions need a non-zero first term.
Ratios and proportions
A ratio compares two quantities — parts of a mix, a map scale, ingredients in a recipe. Simplifying expresses it in the smallest whole numbers that keep the same relationship, which makes ratios easy to compare and scale.
A : B = C : D ⟹ A × D = B × C
A proportion says two ratios are equal. That cross-multiplication rule lets you find a missing term: if three of the four values are known, the fourth is fixed. It is the everyday maths behind scaling drawings, converting units and adjusting recipes.
The ratio 4 : 6 simplifies to 2 : 3. As a proportion, 2 : 3 = 10 : 15, because cross-multiplying gives 3 × 10 ÷ 2 = 15.
Why ratios are so handy
Ratios travel well. A 2 : 3 mix is the same whether you are working in millilitres or gallons, so a recipe or formula scales cleanly to any size. Reading a ratio as "1 : n" or as a decimal often makes the practical step — how much of each — obvious.
Things to watch
- Keep the order. 2 : 3 and 3 : 2 are different relationships.
- Same units. Compare like with like before forming a ratio.
- Cross-multiply to solve. Three known terms always fix the fourth.