Ratio Calculator

What this tool does

The Ratio Calculator reduces ratios such as 1920:1080 to 16:9, solves missing values in proportions, scales recipes or screen sizes, and divides an amount between people in a given ratio. It handles decimals and three or more parts, and shows the arithmetic behind each answer.

Ratios compare quantities: 3 parts flour to 1 part butter, a 16:9 screen, or profits shared 2:3:5 between partners. The same relationship can be written in many equivalent ways, so the practical tasks are reducing a ratio to its simplest form, finding a missing term when two ratios must be equal, and turning a ratio into real amounts.

For simplification the calculator first scales decimal parts to whole numbers (1.5 : 2.5 becomes 15 : 25) and then divides every part by their greatest common divisor, giving 3 : 5. Proportions are solved by cross-multiplication, scaling multiplies each part by the same factor, and splitting divides the total by the sum of the parts. Everything is calculated locally in your browser.

How to use Ratio Calculator

1. Choose the calculation: Simplify a ratio, Solve A : B = C : x, Scale a ratio, or Split a total in a ratio.
2. Type the ratio with colons, for example 1920:1080 or 2:3:5. Commas and spaces also work as separators.
3. For proportions, enter A, B and C; the calculator returns x so that A : B = C : x.
4. For scaling, choose which part you know (its position) and its new value; every other part is scaled to match.
5. For splitting, enter the total; each share, its percentage and a chart are shown.

Tips for better results

• To resize an image while keeping its aspect ratio, use Solve with A:B as the original width and height and C as the new width.
• For recipes, use Scale with the ingredient you are limited by as the known part.
• The unit ratio (smallest part = 1) is handy for comparing mixtures, for example 1 : 2.5 instead of 2 : 5.
• Ratios of three or more parts are supported in Simplify, Scale and Split modes.

Common use cases

• Finding the aspect ratio of a screen, photo or video resolution.
• Scaling a recipe, concrete mix or paint mix to a different batch size.
• Sharing profits, bills or prize money between people in agreed proportions.
• Solving proportion problems in school maths and map-scale questions.

Common mistakes to avoid

• Swapping the order of terms: 3:1 and 1:3 are different ratios.
• Adding a fixed amount to every part to "scale" a ratio; ratios must be multiplied, not added to.
• Splitting a total by the parts themselves rather than by the sum of the parts.