Ratio calculator
Simplify a ratio, see it as percentages and decimals, or scale it to a new value.
How to simplify a ratio
Divide both numbers by their greatest common divisor (GCD). For 12 : 18 the GCD is 6, so 12 ÷ 6 : 18 ÷ 6 = 2 : 3. If the numbers have decimals, multiply both by 10, 100 or 1,000 to make them whole first: 1.5 : 4.5 becomes 15 : 45, which simplifies to 1 : 3.
Worked examples
- Simplify 24 : 36. GCD = 12, so the ratio is 2 : 3.
- Share 100 in the ratio 3 : 2. The parts add to 5, so the shares are 100 × 3/5 = 60 and 100 × 2/5 = 40.
- Scale 3 : 5 so the first number is 21. 21 ÷ 3 = 7, so the second is 5 × 7 = 35.
- Ratio as a fraction. A : B is the fraction A/B; the part of the whole that A represents is A/(A+B).
Ratios in finance and banking
Capital rules are ratios too. The capital adequacy ratio divides a bank's capital by its risk-weighted assets, and the leverage ratio divides Tier 1 capital by total exposure. A ratio of 1 : 10 between capital and assets is the same as a 10% capital-to-assets ratio.
Common mistakes
- Reversing the order: 2 : 3 is not the same as 3 : 2.
- Comparing ratios in different units, such as minutes to hours, without converting first.
- Confusing a ratio with a percentage: 2 : 3 means 40% and 60% of the total, not 2% and 3%.
Frequently asked questions
How do I simplify a ratio?
Divide both numbers by their greatest common divisor. For example 12 : 18 divided by 6 gives 2 : 3.
How do I turn a ratio into a percentage?
Add the parts and divide each part by the total. In 2 : 3 the total is 5, so the parts are 40% and 60%.
How do I find the missing number in a ratio?
Use cross-multiplication: if A : B = C : X then X = B × C ÷ A. The scaled-ratio box above does this for you.
Can a ratio have decimals?
Yes. Multiply both numbers by a power of 10 to make them whole, simplify, and the result is the same ratio.
What is the difference between a ratio and a fraction?
A ratio compares two quantities (A : B). The fraction A/B is the first divided by the second, while A/(A + B) is the share of the whole.
Standard arithmetic definitions. Checked 15 October 2026.