Ratio Calculator

Simplify a ratio, solve a proportion, or scale one up and down — instantly and completely free.

⚡ Runs entirely in your browser

Simplify a ratio

Reduce a ratio to its lowest whole-number terms.

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How the ratio calculator works

Three tools in one — every result is worked out instantly on your device.

1

Simplify

Enter two numbers and we divide both by their greatest common divisor to reach lowest terms, like 16:9.

2

Solve A:B = C:?

Give any three of the four values and we cross-multiply to find the missing one for an equivalent ratio.

3

Scale

Multiply or divide both sides by the same factor to size a ratio up or down while keeping its proportions.

A quick refresher on ratios

A ratio compares two quantities — written A : B — and stays the same when you multiply or divide both sides by the same number. Simplifying means dividing both terms by their greatest common divisor so the ratio is expressed with the smallest whole numbers, for example 8 : 12 becomes 2 : 3. Decimal terms are supported too and are scaled to whole numbers where possible.

A proportion says two ratios are equal, A : B = C : D. Because the cross products are equal (A × D = B × C), knowing any three values lets you solve for the fourth — handy for recipes, maps, mixing, and unit conversions. Scaling keeps a ratio's shape while changing its magnitude: 3 : 4 multiplied by 2 gives 6 : 8, the same proportion at twice the size.

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Private by design. Your numbers never leave your device. Every calculation happens right here in your browser — nothing is uploaded or stored.

Frequently Asked Questions

How do I simplify a ratio to its lowest terms? ▼
Divide both terms by their greatest common divisor (GCD). For example 8 : 12 both divide by 4, giving 2 : 3. The Simplify tab does this automatically, and it also scales decimal terms up to whole numbers where possible.
How do I find a missing term in a proportion? ▼
A proportion says two ratios are equal, A : B = C : D. Because the cross products match (A × D = B × C), knowing any three values lets you solve for the fourth. On the Solve tab, fill in three boxes and leave exactly one empty and the missing term is worked out for you.
What does scaling a ratio do? ▼
Scaling multiplies or divides both terms by the same factor, changing the size while keeping the proportion. For example 3 : 4 multiplied by 2 becomes 6 : 8 — the same ratio at twice the size.
What makes two ratios equivalent? ▼
Two ratios are equivalent when one can be turned into the other by multiplying or dividing both terms by the same number. So 2 : 3, 4 : 6 and 8 : 12 are all the same ratio, because they share the common divisor and reduce to 2 : 3.
Can I use decimals in a ratio? ▼
Yes. Decimal terms are supported and are scaled to whole numbers where it works out cleanly — for example 1.5 : 3 simplifies to 1 : 2. Every calculation runs in your browser and nothing is uploaded.

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