Ratio Calculator — Solve, Simplify and Split

Ratios compare amounts: 2 parts water to 3 parts flour, a 16:9 screen, profits shared 1:2:2. This ratio calculator does the four jobs that come up most: it solves a proportion A : B = C : D when one value is missing, simplifies ratios with two or more terms (including decimals), splits a total amount in a given ratio, and turns a ratio into fractions and percentages of the whole.

How to use this tool

1. Choose what to calculate.
2. To solve a proportion, fill in three of A, B, C and D and leave the unknown empty.
3. To simplify, split or convert, type the ratio with colons, such as 12:18:30.
4. For a split, enter the amount to share out.

Formula

A : B = C : D ⇔ A × D = B × C · Part k = total × term k ÷ (sum of terms)

A ratio is simplified by dividing every term by their greatest common divisor; decimal terms are first multiplied by a power of 10 so they become whole numbers (1.5 : 2.5 → 15 : 25 → 3 : 5). Each term's share of the whole is term ÷ sum of terms.

Example

Solving 3 : 4 = 15 : D gives D = 4 × 15 ÷ 3 = 20. The ratio 12 : 18 : 30 simplifies to 2 : 3 : 5 (all divided by 6), and splitting 900 in that ratio gives 180, 270 and 450.