Ratio Calculator

Find the missing value: A/B = C/D (leave one field empty)

Reduce a ratio to its simplest form

First Number

Second Number

Scale a ratio to a target value for one side

Ratio A

Ratio B

Scale A to

Formula

A/B = C/D → A×D = B×C | Simplified: divide by GCD

How do I solve a proportion?

Cross-multiply: if A/B = C/D, then A×D = B×C. To find a missing value, rearrange: D = B×C/A. For example, 3/4 = 9/D → D = 4×9/3 = 12.

How do I simplify a ratio?

Divide both numbers by their Greatest Common Divisor (GCD). For example, 12:8 → GCD is 4 → 12/4 : 8/4 = 3:2.

Free online percentage calculator. Find percentages, percentage change, percentage difference, and more. Fast, accurate, no signup required.

Free fraction calculator. Add, subtract, multiply, and divide fractions. Simplify fractions and convert between fractions and decimals.