How do I scale a recipe with ratios?

Set up a proportion. If a recipe uses 2 cups flour to 3 eggs and you have 9 eggs, solve 2:3 = x:9, giving x = 6 cups of flour.

Ratio Calculator

Q: How do I simplify a ratio?

Divide both sides by their greatest common divisor. The ratio 18:24 has a GCD of 6, so it simplifies to 3:4.

Q: How do I solve a proportion?

Cross-multiply. For A:B = C:D with one unknown, the products of the diagonals are equal. If 3:4 = 9:x, then 3x = 36, so x = 12.

Simplify a ratio to lowest terms, or solve a proportion (A:B = C:D) for the one value you don't know.

Simplify a ratio

Simplified ratio

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Solve a proportion (A:B = C:D)

Missing value

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How ratios work

Simplify: divide both terms by their GCD
Proportion A:B = C:D → A × D = B × C (cross-multiply)

Worked examples

Simplify 18:24 → divide by GCD 6 → 3:4.

Solve 3:4 = 9:? → 3 × ? = 4 × 9 → ? = 36 ÷ 3 = 12.

Ratios in the real world

Ratios scale things while keeping proportions fixed — recipes, map distances, mixing paint or concrete, aspect ratios, and financial ratios all rely on them. The core trick is cross-multiplication: any proportion with one unknown solves in a single step. To turn a ratio into parts of a whole (like splitting a bill or a batch), add the terms — a 2:3 ratio is 2/5 and 3/5 of the total. Related: the fraction calculator for the same relationships as fractions, and the concrete and paint calculators for mix ratios in practice.

Frequently asked questions

How do I simplify a ratio?

Divide both terms by their GCD. 18:24 → 3:4.

How do I solve a proportion?

Cross-multiply. 3:4 = 9:x → x = 12.

How do I scale a recipe?

Set up a proportion. 2:3 = x:9 → x = 6.

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Last reviewed: July 2026.