How to use the ratio calculator
- Simplify a ratio: enter two or three terms, whole numbers or decimals, to get the simplest whole-number form, such as 12 : 18 : 30 = 2 : 3 : 5.
- Solve A : B = C : x: find the missing value in a proportion, for scaling recipes, maps and models.
- Share an amount: split money, ingredients or time in a ratio, such as 1,000 in the ratio 2 : 3.
Ratio formulas
Simplify: divide every term by their greatest common factor
A : B = C : x → x = B × C ÷ A
Share of an amount = Amount × (its parts ÷ total parts)
Worked examples
Simplify 12 : 18 : 30: the greatest common factor is 6, so it's 2 : 3 : 5.
Solve 3 : 4 = 9 : x: x = 4 × 9 ÷ 3 = 12.
Share 1,000 in the ratio 2 : 3: 5 parts in total, so one part is 200. The shares are 400 and 600.
Decimals: 1.5 : 2.25 is 3/2 : 9/4. Multiplying both by 4 gives 6 : 9, which simplifies to 2 : 3.
For fractions, use the fraction calculator; for percentages of a total, the percentage calculator.
Frequently asked questions
Is a ratio the same as a fraction?
They're related. The ratio 2 : 3 means 2 parts to 3 parts, so the first part is 2/5 of the total, not 2/3.
How do I scale a recipe?
Use Solve. If 4 servings need 300 g of flour, then 4 : 300 = 6 : x gives x = 450 g for 6 servings.
Formulas checked 29 October 2026. How we test our calculators. Check important results, and show your own working where your teacher or exam asks for it.