Proportion Calculator
Solve proportions of the form a / b = c / d by cross-multiplication. Leave one value blank to find the unknown.
Formula
Cross-multiply: if a/b = c/d, then a × d = b × c. Solve for the missing value.
Assumptions
- Values are real numbers. Zero denominators produce an error.
Limitations
- Exactly one value must be left blank to solve.
Worked example
2/3 = 4/x
Cross-multiply: 2 × x = 3 × 4, so x = 6.
Frequently asked questions
Can the unknown be in any position?
Yes. Leave any one of the four values blank and the calculator solves for that position using cross-multiplication.
Last reviewed: 2026-07-22
Category: Math & Algebra
Results are provided for informational purposes only and may not reflect real-world policies, fees, or individual circumstances.
Related calculators
Percentage Calculator
Percentages, changes, time/mass ratios, and OBP
Fraction Calculator
Exact fraction arithmetic with steps