Proportions Solver
Solve proportions: a/b = c/d.
Enter any three values and find the missing fourth.
Cross-multiplication made easy.
Missing Value
Proportions state that two ratios are equal:
a / b = c / d
To solve for a missing value, use cross-multiplication:
a × d = b × c
Solving for each variable:
a = (b × c) / db = (a × d) / cc = (a × d) / bd = (b × c) / a
How to use: Enter any three of the four values and leave one blank. The calculator will find the missing value.
Examples:
- If 2/3 = x/12, then x = (2 × 12) / 3 = 8
- If 5/x = 15/9, then x = (5 × 9) / 15 = 3
- Scale a recipe: 2 cups flour for 12 cookies, how much for 30? → 2/12 = x/30 → x = 5 cups