Formula
A : B = C : x ⇒ x = B × C ÷ ASimplify: divide A and B by GCF(A, B) How it works
A ratio compares two quantities by division. A recipe that uses 3 cups of flour for every 4 cups of milk has a flour-to-milk ratio of 3 : 4. Multiplying or dividing both terms by the same number gives an equivalent ratio, so 6 : 8 and 15 : 20 describe the same mix.
To simplify a ratio, divide both terms by their greatest common factor. If the ratio contains decimals, first multiply both terms by a power of 10 to make them whole numbers: 1.5 : 2.5 becomes 15 : 25, which simplifies to 3 : 5.
A proportion says two ratios are equal. To find a missing term, cross-multiply: in 3 : 4 = 15 : x, 3 × x = 4 × 15, so x = 20. This is the method behind scaling recipes, reading map scales and converting currencies.
Frequently asked questions
Does the order in a ratio matter?
Yes. 3 : 4 (flour to milk) is not the same as 4 : 3. Always keep the terms in the order the question describes.
How do I turn a ratio into a fraction or percentage?
For a part-to-part ratio A : B, the share of A in the total is A ÷ (A + B). For 3 : 4 that is 3/7 ≈ 42.9%.