Ratio Calculator

What is a ratio?

A ratio compares two or more amounts, written as A : B. A ratio of 2 : 3 means that for every 2 of the first thing there are 3 of the second. Ratios are used in recipes, maps, mixing paint or concrete, screen sizes and sharing money.

How to simplify a ratio

Divide every part by the greatest common factor (GCF). For 12 : 18 the GCF is 6, so the ratio simplifies to 2 : 3. If the ratio has decimals, multiply every part by 10, 100 or 1,000 first to make them whole numbers. Our GCF calculator shows how to find the common factor.

How to solve a proportion

A : B = C : D → D = B × C ÷ A

Cross-multiply and divide. If 2 cups of flour make 3 batches, how much flour makes 30 batches? Using batches : flour, 3 : 2 = 30 : D, so D = 2 × 30 ÷ 3 = 20 cups.

How to split a total by a ratio

1. Add the parts of the ratio together.
2. Divide the total by that sum to find the value of one part.
3. Multiply each part of the ratio by that value.

To share $150 in the ratio 2 : 3 : 5, add 2 + 3 + 5 = 10. One part is $15, so the shares are $30, $45 and $75.

Common ratio	Where it is used
16 : 9	Widescreen TVs and monitors
4 : 3	Older screens and many photos
3 : 2	Camera sensors and 4 × 6 prints
1 : 2 : 3	Concrete mix (cement : sand : gravel)
1.618 : 1	The golden ratio

Frequently asked questions

How do you calculate a ratio?

Write the two amounts as A : B and divide both by their greatest common factor. 10 boys and 15 girls is 10 : 15, which simplifies to 2 : 3.

How do you turn a ratio into a percentage?

Divide one part by the sum of all parts and multiply by 100. In 2 : 3, the first part is 2 ÷ 5 = 40%.

How do you turn a ratio into a fraction?

A : B as a fraction comparing the parts is A/B. As a share of the whole, the first part is A/(A + B).

Can a ratio have more than two parts?

Yes. Choose Split a total to divide an amount in a ratio such as 2 : 3 : 5.

Does the order of a ratio matter?

Yes. 2 : 3 and 3 : 2 are different ratios. Keep the order of the items you are comparing.