Ratio Calculator

Ratios describe how two or more quantities relate to one another, and being able to reduce, scale, and solve them is a practical skill across finance, cooking, mapmaking, and statistics. The tool here handles three jobs: it reduces a ratio to its simplest form, rescales it up or down while keeping the proportion intact, and finds a missing term when three of the four values are known. As e-commerce continues its projected 3.5% annual expansion heading into 2026, comparing market shares and dividing resources fairly are everyday tasks that ratios make straightforward.

Behind the scenes, the math relies on a few well-established rules. To reduce a ratio, the calculator finds the greatest common divisor (GCD) of the terms and divides each one by it, so the relationship is preserved while the numbers shrink. Scaling works by multiplying or dividing every term by the same factor. Solving for an unknown uses cross-multiplication: when a/b = c/d, the products ad and bc are equal, which lets you isolate whichever value is missing.

Unit consistency matters more than it first appears. Mixing measurements, such as comparing inches against feet without converting, quietly corrupts the result even when the arithmetic looks clean. Reduction trips people up too: dividing only one side, or stopping before you reach the true greatest common divisor, leaves the ratio half-simplified. Treat a ratio as a relationship rather than a fixed count, since scaling changes both parts together and never just one.