Ratio Calculator

A ratio compares two (or more) quantities, showing how much of one thing there is relative to another — for example, a recipe with a 2:1 ratio of flour to sugar means you use twice as much flour as sugar, no matter how large the batch is.

Simplifying a ratio means reducing both sides to the smallest whole numbers that keep the same proportion. The tool does this by finding the greatest common divisor (GCD) — the largest number that divides both A and B evenly — and dividing both sides by it. For example, 8 and 12 share a GCD of 4, so 8:12 simplifies to 2:3 (8 ÷ 4 = 2, 12 ÷ 4 = 3). If the GCD is 1, the ratio is already in its simplest form.

Equivalent (proportional) ratios are two ratios that represent the same relationship at different scales — like 1:2 and 3:6. To solve for a missing term in A : B = C : D, the tool uses cross-multiplication: since A × D = B × C, rearranging gives D = (B × C) ÷ A.

Worked example — Simplify: a class has 8 boys and 12 girls. The ratio 8:12 simplifies (dividing both by their GCD of 4) to 2:3 — for every 2 boys, there are 3 girls.

Worked example — Equivalent:a paint mix uses a ratio of 4:6 (blue to white). If you want to scale up using 10 units of white, how much blue do you need? Solve 4 : 6 = ? : 10 by cross-multiplying: ? = (4 × 10) ÷ 6 = 6.67 units of blue. Note the tool's second mode is phrased as A : B = C : ?, so you'd enter A = 6, B = 4, C = 10 to get the same answer for the missing blue amount.