Ratio Calculator

Simplify ratios

A ratio compares quantities: 8:12 means 8 parts of one thing for every 12 of another. Simplifying divides every term by their greatest common divisor, so 8:12 becomes 2:3 and 4:8:12 becomes 1:2:3. Simplified ratios are easier to read and compare.

Solve proportions

The second mode finds a missing value in A : B = C : ?. If a recipe uses 2 cups of flour for 3 cups of milk, how much milk goes with 5 cups of flour? 2 : 3 = 5 : ?, so ? = 3 × 5 ÷ 2 = 7.5.

Where ratios come up

• Cooking: scaling a recipe up or down.
• Screens and images: aspect ratios such as 16:9, 4:3 and 1:1. A 1920 × 1080 screen simplifies to 16:9.
• Mixing: concrete, paint, fertiliser, cleaning solutions or two-stroke fuel, often written as 1:4 or 50:1.
• Maps and models: a 1:50,000 map means 1 cm on paper is 50,000 cm (500 m) on the ground.
• Finance: debt-to-income, current ratio and other financial ratios.
• Sharing: dividing profit or costs between partners in proportion to what they put in.

Splitting an amount by a ratio

To divide 1,200 in the ratio 1:2:3, add the parts (1 + 2 + 3 = 6), work out one part (1,200 ÷ 6 = 200), then multiply: 200, 400 and 600.