Ratio Calculator

Work with ratios two ways. This free ratio calculator simplifies a ratio to lowest terms, or solves a proportion (A:B = C:D) for the missing value — decimals supported.

Mode
:

Enter a ratio like 10 : 15 and it reduces to lowest terms by dividing both sides by their greatest common divisor. Decimals are supported.

Simplified ratio
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Enter your values

A ratio compares two quantities. Simplifying keeps the same proportion with the smallest whole numbers; solving a proportion finds an unknown that keeps two ratios equal.

Use this free ratio calculator to simplify a ratio to its lowest terms, or to solve a proportion. Enter a ratio like 10 : 15, or fill in three of four values in A : B = C : D to find the missing one.

What this ratio calculator does

A ratio calculator works with ratios two ways. Simplify mode reduces a ratio to its smallest whole numbers; solve mode finds an unknown in a proportion (A : B = C : D) by cross-multiplying.

How to simplify a ratio

Divide both terms by their greatest common divisor (GCD)

For 10 : 15, the GCD is 5, so it reduces to 2 : 3. Decimal ratios are scaled up first — for example 1.5 : 3 becomes 1 : 2.

How to solve a proportion

In a proportion A : B = C : D, the cross-products are equal: A × D = B × C. So if 2 : 3 = 4 : x, then x = (3 × 4) ÷ 2 = 6. Leave the unknown blank and the calculator solves it.

Ratio examples

Ratio Simplified
4 : 6 2 : 3
8 : 32 1 : 4
10 : 15 2 : 3
0.25 : 0.75 1 : 3

How to use the ratio calculator

  1. Choose simplify or solve.
  2. To simplify, enter both terms of the ratio.
  3. To solve, enter three values and leave the unknown blank.

Ratio FAQ

How do I simplify a ratio?

Divide both terms by their greatest common divisor. For 10 : 15 the GCD is 5, so it simplifies to 2 : 3. The calculator does this automatically.

How do I solve a proportion?

In A : B = C : D the cross-products match (A × D = B × C). Leave the unknown blank and the calculator solves it — for 2 : 3 = 4 : x, x = 6.

Can it simplify ratios with decimals?

Yes. It scales decimal terms up to whole numbers first, so 1.5 : 3 becomes 1 : 2 and 0.25 : 0.75 becomes 1 : 3.

What's the difference between a ratio and a fraction?

A ratio compares two quantities (2 : 3), while a fraction expresses a part of a whole (2/5). They're closely related, and the calculator shows the fraction form too.

How do I convert a ratio to a percentage?

Divide one term by the total. In 2 : 3 the total is 5, so the first part is 2 ÷ 5 = 40%. The calculator shows both percentages.

Is the ratio calculator free?

Yes, this ratio calculator is completely free, needs no sign-up, and gives instant results in your browser.

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