About the Ratio Calculator
This does the two things people most need with ratios: reduce a ratio to its simplest form, and solve a proportion for a missing value. Ratios come up in recipes and mixing (paint, fuel, concrete), scaling drawings and models, aspect ratios, dividing money or shares, and school maths. Enter your numbers and it simplifies or solves instantly. Used as a ratio solver, it finds the missing term of a proportion for you — enter three of the four values and it works out the fourth.
Dividing a share as a percentage instead of a ratio? Try the Percentage Calculator.
How it works
Simplify: it finds the greatest common divisor (GCD) of the two numbers and divides both by it, giving the ratio in lowest whole-number terms — so 16 : 9 stays 16 : 9, but 20 : 30 reduces to 2 : 3. Decimals are scaled to whole numbers first. It also shows the ratio as a decimal (X : 1).
Solve a proportion: for A : B = C : ?, it uses cross-multiplication — the missing value is B × C ÷ A. So 3 : 4 = 9 : ? gives 12, because the two ratios must be equal.
Assumptions and behaviour
- Simplifying uses the GCD to reduce to lowest whole-number terms.
- Decimal inputs are scaled up to integers before reducing, so 1.5 : 3 becomes 1 : 2.
- The proportion solver finds the fourth term by cross-multiplication (B × C ÷ A).
- Results are shown to six decimal places where not whole.
Limitations
- Simplifying works best with whole numbers or simple decimals; very long or irrational decimals may not reduce to a tidy ratio.
- The proportion solver needs A, B and C, and A can't be zero (you'd be dividing by zero).
- It works with two-part ratios (A : B); it doesn't simplify three-part ratios like A : B : C in one step — simplify pairs individually, or use the Fraction Calculator for a single A/B reduction.
- It assumes the proportion is a simple direct one (A : B = C : ?), not an inverse proportion.
Privacy
The calculation runs entirely in your browser. Nothing is uploaded or stored.
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