How do I simplify a ratio to its lowest terms?

Divide both terms by their greatest common divisor (GCD). The Ratio Calculator does this automatically — for example it reduces 1920:1080 to 16:9 — and also shows the decimal and percentage equivalents.

How do I solve a ratio with a missing value?

Use the proportion solver. Enter three of the four values in A:B = C:D, leave the unknown box blank, and press Solve. It uses cross-multiplication, where A times D equals B times C.

Can the ratio calculator handle decimals?

Yes. If you enter decimal terms, the calculator scales them up to whole numbers and then reduces the ratio to its simplest whole-number form.

What does the ratio as a percentage mean?

It expresses the first term as a percentage of the combined total. For a 3:1 ratio, the first part is 75% of the whole and the second part is 25%.

What is a proportion?

A proportion is a statement that two ratios are equal, such as 3:4 = 9:12. Proportions let you scale recipes, maps, models and mixtures up or down while keeping the relationship constant.

Ratio Calculator 2026 — Simplify & Solve Ratios

About the Ratio Calculator

The Ratio Calculator does two jobs: it simplifies a ratio to its lowest whole-number terms, and it solves proportions of the form A : B = C : D when one value is unknown. It also expresses a ratio as a decimal and as a percentage of the total — handy for recipes, scale models, aspect ratios, mixing fluids, finance and maths homework.

How ratios are simplified

A ratio is simplified by dividing both terms by their greatest common divisor (GCD). For example, 16 : 9 is already in lowest terms (GCD 1), while 1920 : 1080 simplifies to 16 : 9. For decimal inputs the calculator scales both terms to whole numbers first, then reduces.

Solving proportions

Two ratios are equal when their cross-products match: A × D = B × C. Leave one of the four boxes blank and the calculator solves for it. For example, 3 : 4 = 9 : ? gives 12, because 3 × 12 = 4 × 9.

Worked example

A recipe for 4 people uses 200 g of rice. For 6 people, solve 4 : 200 = 6 : ? → 300 g. The same method scales drawings, maps and screen resolutions.

Frequently Asked Questions

How do I simplify a ratio? Divide both numbers by their greatest common divisor. The calculator does this automatically and also shows the decimal and percentage form.

How do I solve a ratio with an unknown? Use the proportion solver: enter three values, leave the unknown blank, and it applies cross-multiplication.

Can it handle decimals? Yes — decimal terms are scaled to whole numbers before simplifying.

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Important Note: This tool is intended to provide estimates and should not be used as a substitute for professional advice. Information generated by these calculators may be incomplete and does not account for all individual circumstances. Always seek the counsel of a certified expert (such as a financial advisor, healthcare provider, or licensed engineer) before taking action based on these results.

Related Calculators

Fraction Calculator — Add, subtract, multiply and simplify fractions.
Percentage Calculator — Percentage of a number and percentage change.
Average Calculator — Mean, median, mode and range of a data set.

➗ Ratio Calculator

Simplify a ratio

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