Ratio Calculator

Simplify ratios, solve for a missing term in a proportion and split an amount in any ratio, all in one place.

1. Simplify a ratio

2. Solve a proportion A : B = C : D (leave one box empty)

: = :

3. Divide an amount in a ratio

Total in the ratio :

What is a ratio and how do you calculate it?

A ratio compares two quantities: 12 boys to 18 girls is the ratio 12:18, which simplifies to 2:3 by dividing both numbers by their greatest common factor, 6. Ratios are used for recipes, maps and scale models, mixing paint or concrete, and splitting money or profits. This ratio calculator simplifies a ratio, solves a missing term in a proportion and divides an amount in a given ratio.

How to simplify a ratio

Divide both terms by their greatest common factor (GCF). 12:18 has a GCF of 6, so it becomes 2:3. If one term is zero or the numbers are decimals, multiply both by the same power of 10 first to make them whole numbers.

How to solve a proportion

Two ratios are equal when A ÷ B = C ÷ D, which means A × D = B × C (cross multiplication). To find the missing D: D = B × C ÷ A. Example: 3:4 = 9:D gives D = 4 × 9 ÷ 3 = 12.

How to split an amount in a ratio

Add the parts, divide the total by that sum, then multiply by each part. Splitting 100 in the ratio 3:2: 3 + 2 = 5 parts, so each part is 20 and the shares are 60 and 40.

Use	Example	Result
Recipe scaling	Flour:sugar 5:2 with 500 g flour	200 g sugar
Map scale	1:50,000, 4 cm on the map	2 km in real life
Concrete mix	1:2:3 cement:sand:gravel, 12 parts total	2, 4 and 6 parts
Profit split	$9,000 in the ratio 5:3:1	$5,000, $3,000 and $1,000

How to use the ratio calculator

Type the two numbers of the ratio to simplify it.
For a proportion, fill three of the four boxes and leave the missing one empty.
To split an amount, enter the total and the two parts of the ratio.

Frequently asked questions

How do I simplify a ratio?

Divide both numbers by their greatest common factor. 12:18 becomes 2:3 because both are divisible by 6.

How do I find the missing number in a ratio?

Use cross multiplication: for A:B = C:D, D = B × C ÷ A. For 3:4 = 9:D, D = 12.

How do I divide a number in a ratio?

Add the ratio parts, divide the total by that sum and multiply by each part. 100 in the ratio 3:2 gives 60 and 40.

Can a ratio have decimals?

Yes, but to simplify it, multiply both terms by 10, 100 and so on until both are whole numbers.

What is the difference between a ratio and a fraction?

A ratio compares parts to parts (3:2), while a fraction compares a part to the whole (3/5). In a 3:2 split, the first share is 3/5 of the total.

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