Ratio Calculator

Ratio Calculator does the three things people actually need from ratios: reduce one to its lowest terms, find a missing value in a proportion, and scale a ratio up or down to a new total.

Simplifying works by dividing every term by the greatest common divisor of all of them, which is why 48:36:12 becomes 4:3:1 rather than being reduced a pair at a time. The calculator handles ratios of three or more terms for this reason; many only take two, which is where recipe and mixing ratios fall over.

Solving a proportion means finding the value that keeps two ratios equal: given 3:4 = 9:x, the answer comes from cross-multiplication, x = 4 x 9 / 3 = 12. This is the calculation behind map scales, recipe conversion, currency-free unit scaling and most of the ratio questions that appear in exams.

Scaling to a total is the one people most often do by hand and get wrong. Splitting 2,400 in the ratio 5:3:4 means dividing by the sum of the parts, twelve, then multiplying each part by the result: 1,000, 600 and 800. The calculator also handles the remainder honestly when the total does not divide evenly, rather than silently rounding each share and producing a set that does not add up.

Everything is worked out inside your browser. Nothing you enter is uploaded, logged or stored, which matters for the financial calculators in particular: the figures you put into them are nobody else's business.

• Simplify ratios of two, three or more terms
• Solve a proportion for any missing term
• Split a total in a given ratio, with the remainder handled honestly
• Converts to fractions, decimals and percentages
• Accepts decimals and converts them to whole-number ratios
• Shows the greatest common divisor used
• Runs in your browser

The ratio calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Scaling a recipe up or down
• Splitting a bill, a profit or a prize in agreed shares
• Working with map and model scales
• Mixing paint, fuel or chemicals to a specification
• Maths homework where the working must be shown