Ratio Calculator
Simplify a ratio, solve a proportion such as 3 : 4 = 9 : ?, or divide a total in a ratio, exactly.
Your ratio
Filled in with example values. Replace them with your own.
Whole numbers, decimals (1.5) or fractions (1/2).
Results update as you type.
Result
12 : 18 : 30 = 2 : 3 : 5
Simplest form
2 : 3 : 5
How it’s calculated
Divide by the greatest common divisor
12 : 18 : 30 ÷ 6 = 2 : 3 : 5
How the ratio calculator works
A ratio compares amounts by how many times one contains the other. The calculator simplifies a ratio of two to four parts, solves a proportion with one missing value, or divides a total in a given ratio. Parts can be whole numbers, decimals or fractions, and every answer is exact.
The formulas
Simplest form: each part ÷ GCD of all parts
A : B = C : x → x = B × C ÷ A
Share = Total × Part ÷ Sum of parts
Worked examples
- 12 : 18 : 30 ÷ 6 = 2 : 3 : 5; 1.5 : 2 = 3 : 4.
- 3 : 4 = 9 : ? gives 4 × 9 ÷ 3 = 12.
- 600 in 1 : 2 : 3: 6 parts of 100, so 100, 200 and 300.
Frequently asked questions
How do I simplify a ratio?
Divide every part by their greatest common divisor. 12 : 18 : 30 are all divisible by 6, giving 2 : 3 : 5. If a part is a decimal or a fraction, first multiply every part by the same number to make them whole.
How do I solve a proportion?
In A : B = C : ?, the missing value is B × C ÷ A, often called cross-multiplying. For 3 : 4 = 9 : ?, it is 4 × 9 ÷ 3 = 12.
How do I divide an amount in a ratio?
Add up the parts to find the total number of shares, divide the amount by it to get one share, then multiply by each part. 600 in 1 : 2 : 3 is 6 shares of 100, so 100, 200 and 300.
Why are some shares shown with brackets?
Some amounts do not divide evenly. 100 in 1 : 2 gives 33.(3) and 66.(6), where the digit in brackets repeats. If you are sharing money, round to the cent and adjust one share so the total still matches.