Ratio Calculator
Simplify a ratio to its lowest terms or solve a proportion for the missing value. Enter A:B to reduce it, or A:B = C:D with one blank to solve.
How it works
Ratio and proportion
Simplify: divide A and B by their greatest common divisor (GCD) Proportion: A / B = C / D Solve: C = A × D / B or D = B × C / A
A ratio compares two quantities. To simplify, divide both sides by their greatest common divisor. A proportion states that two ratios are equal; cross-multiplying (A × D = B × C) lets you solve for any missing term.
Worked example
The ratio 18 : 24 simplifies by dividing both by their GCD (6) to give 3 : 4. To solve 18 : 24 = 6 : D, cross-multiply: D = 24 × 6 / 18 = 8.
Frequently asked questions
How do I simplify a ratio?
Find the greatest common divisor (GCD) of both numbers and divide each by it. For 18 : 24, the GCD is 6, so the simplified ratio is 3 : 4.
What is a proportion?
A proportion is a statement that two ratios are equal, such as 1 : 2 = 3 : 6. If one value is unknown, cross-multiplication solves it: the product of the outer terms equals the product of the inner terms.
Can I use decimals in a ratio?
Yes. The calculator accepts decimals and simplifies or solves the same way. Simplification works most cleanly with whole numbers, though.