Ratio Calculator

Solve ratio problems in three ways: find the missing value in A : B = C : D, simplify a ratio to its lowest terms (also with decimals), or split a total in a given ratio. Results include the 1 : n form and percentage split.

This tool runs entirely in your browser.

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How to use the Ratio Calculator

1Choose what to calculate: a missing value, a simplified ratio or a split.
2Enter the known numbers — for a proportion, leave exactly one of A, B, C, D empty.
3Read the answer and the other forms of the ratio.

What is the Ratio Calculator?

A proportion A : B = C : D is solved by cross-multiplication: A × D = B × C. For example 3 : 4 = 9 : ? gives ? = 4 × 9 ÷ 3 = 12.

To simplify, decimals are first scaled to whole numbers and then divided by their greatest common divisor, so 1.5 : 2 becomes 3 : 4. Splitting 700 in the ratio 3 : 4 gives 300 and 400.

Frequently asked questions

What is the 1 : n form?

It rescales the ratio so the first part is 1 — handy for maps and model scales. 3 : 4 is 1 : 1.333…

Can I use it for recipes?

Yes. To scale 250 g flour for 4 people to 6 people, solve 4 : 250 = 6 : ? — the answer is 375 g.

Is the Ratio Calculator free and private?

Yes. The Ratio Calculator is free, needs no account, and runs entirely in your browser. What you type is never sent to a server or stored.

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