Solve A:B = C:D instantly — and reduce any ratio to its simplest form
Enter Three Values — Tap Any Field to Solve For It
The highlighted field (red outline) is being solved for. Click any other field to solve for it instead.
Quick examples
Result
Formula: A × D = B × C (cross-multiplication). To find the missing term, rearrange: e.g. D = (B × C) / A.
A ratio calculator solves proportions and reduces ratios in seconds. Use the Solve A:B = C:D mode to find any missing term with cross-multiplication — perfect for scaling recipes, mixing solutions, or map reading. Switch to Simplify mode to reduce any ratio to its lowest terms using the Greatest Common Divisor. Works with whole numbers and decimals alike.
Enter the three known values in the A:B = C:D fields and click the field you want to solve for — it will be highlighted. The calculator uses cross-multiplication (A × D = B × C) to find the missing number instantly.
Both terms are divided by their Greatest Common Divisor (GCD). For example, 24:36 has a GCD of 12, so the simplified ratio is 2:3. The calculator handles decimal inputs too, by scaling up before finding the GCD.
Yes. If a recipe calls for 2 cups of flour per 1 cup of sugar and you want 6 cups of flour, set A=2, B=1, C=6 and solve for D to find you need 3 cups of sugar.
A ratio (e.g. 3:4) compares two quantities. A proportion is an equation stating that two ratios are equal (e.g. 3:4 = 9:12). This calculator handles both: simplify a single ratio, or solve a full proportion for its missing term.