Ratio Calculator
Free ratio calculator — simplify a ratio to its lowest terms or solve a proportion A:B = C:D for the missing value.
Everyday Uses
Recipes
Scale ingredient ratios up or down while keeping proportions exact.
Maps & models
Work with scale ratios like 1:100 and solve for real or model sizes.
Mixing
Get the right dilution — fuel:oil, paint, or cleaning solutions.
Aspect ratios
Simplify width:height and solve proportions for screens or images.
Frequently Asked Questions
How do you simplify a ratio?
Divide both sides of the ratio by their greatest common divisor (GCD). For 16 : 12, the GCD is 4, so the ratio simplifies to 4 : 3. If the terms are decimals, first multiply both by a power of ten to make them whole numbers, then divide by the GCD.
How do you solve a proportion?
A proportion states that two ratios are equal: A : B = C : D, which means A ÷ B = C ÷ D. Cross-multiply to solve for a missing term — for example if 3 : 4 = x : 20, then x = (3 × 20) ÷ 4 = 15. Leave one value blank in this calculator and it solves for it automatically.
How do you scale a ratio?
Multiply or divide every term by the same number. To scale a recipe of 2 : 3 up by four, multiply both terms to get 8 : 12. To express any ratio "per one", divide both terms by the first — 4 : 3 becomes 1 : 0.75.