MATH · PROPORTION
Proportion Calculator
Solve a proportion a/b = c/d for any unknown term. Enter the three known values and select which one is missing.
D =
6
D = 6 (from a/b = c/d)
About This Calculator
A proportion states that two ratios are equal: a/b = c/d. When you know three of the four values you can always find the fourth by cross-multiplying. Select which term is unknown and enter the three known values.
How It Works
Select the unknown term (a, b, c, or d), then fill in the three known values. The calculator solves using cross-multiplication. Results are rounded to 4 decimal places.
The Formula
a × d = b × c Solve for d: d = (b × c) / a Solve for c: c = (a × d) / b
- a, b, c, d
- the four terms of the proportion a/b = c/d
Frequently Asked Questions
- What is a proportion?
- A proportion states that two fractions are equal — a/b = c/d. Proportions appear in scaling problems, unit conversions, map reading, and recipe scaling.
- Which term should I set as unknown?
- Whichever term you are trying to find. The calculator will solve for that one using the three values you provide.
- Can any term be zero?
- The term in the denominator of the unknown's solving formula cannot be zero. For example, a cannot be zero when solving for d, because d = (b×c)/a would divide by zero.