Proportion Calculator
Solve proportion equations for an unknown value.
Runs locally in your browser
Your inputs are processed locally in your browser and are not uploaded or stored by us.
Solve proportion equations (a / b = c / d) for any single unknown value.
How to solve a proportion
- Select which variable you want to solve for (a, b, c, or d).
- Enter the numeric values for the other three positions.
- The calculator will use cross-multiplication to determine the unknown value.
Proportion Formulas
Solve for a: a = (b × c) / d
Solve for b: b = (a × d) / c
Solve for c: c = (a × d) / b
Solve for d: d = (b × c) / a
Proportions are solved using direct cross-multiplication. This tool solves specifically for the single unknown variable rather than acting as a symbolic algebraic solver.
Solving x / 4 = 6 / 8
Unknowna (x)
b4
c6
d8
x = (b × c) / d
x = (4 × 6) / 8
x = 24 / 8
Result: x = 3
Notes
- The calculator accepts positive numbers, negative numbers, and decimals.
- Zero is a valid input unless the selected formula requires division by zero (e.g., trying to solve for "a" when "d = 0").
- The calculator rejects a selected solve operation when that direct calculation would require division by zero.
- Unlike exact-fraction tools, the proportion result may evaluate to a floating-point decimal.
- Your inputs are processed locally in your browser and are not uploaded or stored by us.