How do you simplify a ratio?

Divide both terms by their greatest common divisor. For example, 16 : 9 is already simplest, while 4 : 8 reduces to 1 : 2. The calculator does this automatically.

How do I solve a proportion like A : B = C : ?

Cross-multiply — the missing term equals B × C ÷ A. For example, 3 : 4 = 9 : ? gives 4 × 9 ÷ 3 = 12. Use the solve mode to compute it for you.

What is the difference between a ratio and a proportion?

A ratio compares two quantities, like 3 : 4. A proportion states that two ratios are equal, like 3 : 4 = 9 : 12. This calculator both simplifies a single ratio and solves a proportion for an unknown term.

Can it handle decimal inputs?

Yes. You can enter decimals such as 2.5 : 5; the proportion solver computes the missing term by cross-multiplication, and simplification works on whole-number ratios via their greatest common divisor.

How do I convert a ratio to a decimal or percentage?

Divide the first term by the second. For 16 : 9 that is 16 ÷ 9 ≈ 1.78, or as a percentage of the total, 16 ÷ (16 + 9) ≈ 64%.

What does it return for 0 in the ratio?

Simplifying a ratio with a zero term still works (e.g. 0 : 5 → 0 : 1), but solving a proportion where the divisor would be zero is undefined, so make sure the known first term is not zero.

Ratio Calculator — Gera Tools

Q: Is my data sent anywhere?

No. Everything is computed in your browser with plain arithmetic. Nothing you enter is uploaded or stored.

A ratio compares two quantities; a proportion states two ratios are equal. This calculator does both common jobs: it simplifies a ratio to its lowest terms, and it solves a proportion for a missing term — useful for recipes, scale models, maps, mixing, finance, and school maths.

How it works

Simplify mode reduces a ratio A : B by dividing both terms by their greatest common divisor (GCD), found with the Euclidean algorithm. If the GCD is 1 the ratio is already in lowest terms; otherwise both sides shrink by the same factor, preserving the proportion.

Solve mode treats a proportion A : B = C : ? and finds the unknown by cross-multiplication. Since A/B = C/x rearranges to x = B × C ÷ A, the calculator plugs in your three known values and returns the fourth.

Example

Simplify 18 : 24. The GCD of 18 and 24 is 6, so dividing both gives 3 : 4.

Solve the proportion 3 : 4 = 9 : ?. Cross-multiplying, the missing term is 4 × 9 ÷ 3 = 12, so the complete proportion is 3 : 4 = 9 : 12.

Input	Mode	Result
4 : 8	Simplify	1 : 2
18 : 24	Simplify	3 : 4
3 : 4 = 9 : ?	Solve	12
5 : 2 = ? : 10	Solve	25

Everything is computed in your browser with plain arithmetic — nothing you enter is uploaded.