The Ratio Calculator solves proportions of the form A : B = C : D when one value is missing, and enlarges or shrinks a ratio by a factor.
D = 800
| D | 800 |
| Ratio | 3 : 4 = 600 : 800 |
| Result | 100 : 112 |
A ratio compares two quantities, written A : B or A/B. A 3 : 4 ratio means for every 3 of the first there are 4 of the second. Ratios are used in recipes, maps and scale models, mixing concrete or paint, screen aspect ratios (16 : 9) and finance.
Two equal ratios form a proportion, A : B = C : D, and cross-multiplying gives A × D = B × C. Any one missing value can be found: D = B × C ÷ A.
Worked example (defaults): 3 : 4 = 600 : D gives D = 4 × 600 ÷ 3 = 800.
Divide both terms by their greatest common factor to simplify: 250 : 280 becomes 25 : 28. Multiplying or dividing both terms by the same number keeps the ratio equal, which is how images and recipes are resized.
Is 3:4 the same as 4:3? No, order matters.
How do I turn a ratio into a percentage? A ÷ (A + B) × 100% gives A's share.
What is the golden ratio? About 1.618 : 1.