Ratio calculator

Four ratio tools in one place. Each box answers as you type and shows the working.

By the Calcist team · Checked against known answers · Updated October 27, 2026

Private: calculated on your device. Nothing you type is sent anywhere.

Next: Working with fractions of the whole? The fraction calculator and percentage calculator show every step.

How ratios work

A ratio compares amounts. 3 : 2 means "3 of the first for every 2 of the second". Multiplying or dividing every term by the same number gives an equal ratio, so 12 : 18, 6 : 9 and 2 : 3 are the same.

Simplify: divide every term by their greatest common factor
Proportion: A : B = C : D means A × D = B × C
Split a total T in a : b: shares are T × a ÷ (a + b) and T × b ÷ (a + b)

Worked examples

Simplify 1.5 : 2.25. Multiply both by 100 to clear the decimals: 150 : 225. The greatest common factor is 75, so the ratio is 2 : 3.
Solve 3 : 4 = 15 : x. Cross-multiply: 3x = 4 × 15 = 60, so x = 20.
Split $500 in the ratio 3 : 2. There are 3 + 2 = 5 parts, each worth $500 ÷ 5 = $100. The shares are $300 and $200.
3 : 5 as a fraction. 3 ÷ 5 = 3/5 = 60%. As parts of a whole, 3 is 3/8 = 37.5% and 5 is 5/8 = 62.5%.

Two ways to turn a ratio into a fraction

"The ratio of boys to girls is 3 : 5" can mean boys ÷ girls = 3/5, or boys as a share of everyone = 3/8. Both are correct answers to different questions, so the converter shows both. Read the question to see which one it wants.

Limitations

Ratio terms here must be positive. Negative ratios don't have a common everyday meaning.
When splitting money, shares can come out with fractions of a cent. Round them so they still add up to the total.

Sources

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

12:18 rows labelled As 1 : x = 1 : 1.5 ✓
12:18 simplifies to 2 : 3 ✓
1.5:2.25 simplifies to 2 : 3 ✓
4:6:10 simplifies to 2 : 3 : 5 ✓
3 : 4 = 15 : x gives x = 20 ✓
$500 split 3:2 is 300 and 200 ✓
60% as part : rest is 3 : 2 ✓
A ratio with a 0 term is rejected ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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Questions people ask

How do I simplify a ratio?

Divide every term by the largest number that divides them all. For 12 : 18 that's 6, giving 2 : 3. If there are decimals, multiply every term by 10, 100 or 1,000 first to make them whole numbers.

How do I solve a ratio with a missing number?

Write it as A : B = C : D and cross-multiply: A × D = B × C. Then divide to get the unknown alone. For 3 : 4 = 15 : x, x = 4 × 15 ÷ 3 = 20.

How do I split money in a ratio?

Add the parts of the ratio, divide the total by that sum to get the value of one part, and multiply by each person's parts. $500 in 3 : 2 gives $300 and $200.

How do I convert a ratio to a percent?

Divide the first term by the second and multiply by 100: 3 : 5 is 60%. If you want the first term's share of the whole, divide by the sum instead: 3 ÷ 8 = 37.5%.

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