Math & science
Proportion Calculator
Solve the fourth value in a direct or inverse proportion using three known values.
Interactive calculator
Solve direct and inverse proportion
Use three known values to find the fourth value in a direct or inverse proportion setup.
Results
Solved value
15
Solves a:b = c:x
How to use it
- 01Choose direct or inverse proportion mode.
- 02Enter the three known values in the relation.
- 03Read the solved fourth value and use it in your equation or word problem.
Result guide
- Direct proportion means values rise or fall together in the same ratio.
- Inverse proportion means one value rises while the other falls so the product stays constant.
- This calculator requires non-zero values for the three known inputs.
About this calculator
Proportion problems appear constantly in classroom math, scaling, recipes, and real-world comparison questions. A dedicated solver helps users jump straight to the missing value.
Switching between direct and inverse proportion on the same page makes the tool more useful than a one-mode worksheet helper.
Frequently asked questions
How do I know if the problem is direct or inverse proportion?
If two quantities change together in the same direction, it is usually direct proportion; if one rises while the other falls, it is often inverse proportion.
Why use three known values?
Because the goal is to solve the fourth unknown value from a four-part proportion setup.
Can proportion results be decimals?
Yes. The solved value does not need to be a whole number.
Method and limitations
This calculator uses the formula and assumptions described on this page. We do not claim independent professional review. Direct references will be listed here when they support a specific rule or data source used by this calculator.
Results are estimates for general information. Verify current rules and assumptions before making financial, tax, or health decisions.
Read our Editorial and Verification Policy →Related calculators
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