How to solve a proportion
A : B = C : D → D = B × C ÷ A
Cross-multiply and divide. For 16:9 = 1920:D, D = 9 × 1920 ÷ 16 = 1080.
Simplifying a ratio
Divide both sides by their greatest common factor. 1920:1080 divides by 120, giving 16:9. Ratios with decimals are first multiplied by 10, 100, and so on until both sides are whole numbers.
Everyday uses
| Use | Example |
|---|---|
| Recipes | 2 cups flour : 3 eggs, scaled to 5 eggs = 3.33 cups |
| Screens and photos | 16:9, 4:3, 3:2 aspect ratios |
| Maps | 1:24,000 means 1 inch = 24,000 inches (2,000 ft) |
| Mixing | 1:4 concentrate to water |
Frequently asked questions
What's the difference between a ratio and a fraction?
A ratio compares two parts (3 boys to 2 girls, 3:2). A fraction compares a part to the whole (3 of 5 children are boys, 3/5).
Can a ratio have more than two parts?
Yes, such as 1:2:3 for a mix. This calculator handles two-part ratios.