5 min read
2026-02-08
A tool for solving proportions of the form a/b = c/d, where one value is unknown. Also supports percentage calculations and scaling.
A proportion is an equality of two ratios: a/b = c/d. The key property: the product of the extremes equals the product of the means (a × d = b × c).
Enter three known values of the proportion
Leave one field empty — that is the unknown
Click Calculate
Get the answer with the solution formula
| Problem type | Example |
|---|---|
| Find an unknown term | 3/5 = x/20, x = ? |
| Percentage problems | 15% of 200 = ? |
| Map scale | 1:50000, 3 cm = ? m |
| Recipe scaling | For 4 servings — 200 g, for 6 — ? |
To verify a proportion, compute the product of the extremes and the product of the means. If they are equal, the proportion is correct.
The calculator supports both kinds and picks the right formula automatically.
See also: Fraction Calculator, Equation Solver, Statistics