Ratio Calculator

A ratio calculator reduces a ratio to its simplest whole-number form and solves proportions where one value is unknown. Enter two numbers such as 1920 and 1080 and it returns the reduced ratio 16 : 9, along with the decimal value and the percentage each part represents. Switch to proportion mode, leave one field of A : B = C : D blank, and it cross-multiplies to fill in the missing number.

A ratio expresses how two quantities relate in size, written as A : B and read as "A to B". Reducing a ratio means dividing both terms by their greatest common divisor until no whole number divides both, so 8 : 12 becomes 2 : 3. The reduced form is the clearest way to state a relationship because it uses the smallest numbers that carry the same meaning, which is why recipes, screen dimensions, map scales, and mixing instructions are almost always given in lowest terms.

The second job of the tool is solving a proportion. A proportion is a statement that two ratios are equal, A : B = C : D, and it is the everyday tool for scaling something up or down while keeping the shape the same. If a recipe uses 2 cups of flour for every 3 eggs and you have 9 eggs, the proportion 2 : 3 = x : 9 tells you to use 6 cups. The calculator handles that cross-multiplication for you: type the three known values, leave the fourth blank, and it solves for it and shows the working so you can check it.

Decimal inputs are supported throughout. A ratio like 2.5 : 5 is scaled to whole numbers before the greatest common divisor is taken, so it reduces cleanly to 1 : 2 rather than leaving a fractional term. Proportions accept decimals too, which matters for money, measurements, and unit conversions where the numbers rarely come out even. Every result is rounded to a sensible precision and the raw decimal is shown alongside the reduced ratio.

Everything runs in your browser with JavaScript. Nothing is uploaded, there is no account, and the tool keeps working offline once the page has loaded. The arithmetic is instant, so you can adjust the numbers and watch the reduced ratio and the solved value update as you type, which makes it quick to compare a few options before committing to one.