⚖️ Ratio Calculator

Simplify a ratio, or solve a proportion for a missing value.

About this tool

Simplifies a ratio A:B down to its lowest terms using the greatest common divisor, and separately solves a proportion of the form A:B = C:D for the missing fourth value using cross-multiplication.

Two related but distinct ratio tasks, both common in cooking, scaling recipes, mixing solutions, and map-scale problems.

Worked example

8:12 simplifies to 2:3. Solving 2:5 = 10:? gives ? = 25.

How to use it

For simplifying, enter both parts of the ratio and press Simplify.
For solving a proportion, enter the three known values (A, B, C) and press Solve — the missing fourth value (D) is calculated automatically.

Tips

A ratio and a fraction are closely related — 2:3 simplifies the same way 2/3 does, using the same greatest-common-divisor logic.
Proportions are the standard tool for scaling a recipe up or down while keeping ingredient ratios constant.
If your ratio includes decimals, the simplifier switches to a decimal-to-1 format instead of whole-number lowest terms, since GCD-based simplification only works cleanly on integers.

FAQ

What's the difference between a ratio and a proportion?

A ratio compares two numbers (like 2:3); a proportion states that two ratios are equal (like 2:3 = 4:6) — this tool handles simplifying the first and solving the second.

Can I use this to scale a recipe?

Yes — set up your original ratio as A:B and your new known quantity as C, and the calculator solves for the matching quantity D.

Does it work with decimal ratios?

Yes, though the simplification step displays decimal ratios as a "decimal : 1" form rather than whole-number lowest terms, since true simplification requires integers.

From the blog: getting the most out of this tool

Recipe scaling is the single most common real-world use of a proportion solver — you know the original ratio of flour to sugar, you know how much flour you actually have, and you need the matching sugar amount without doing the cross-multiplication by hand.

We built the simplifier and the proportion solver as two separate mini-tools on one page because they solve genuinely different problems, even though both live under the umbrella of "ratio math."