About this tool
Solve A / B = C / x for the missing value (rule of three).
Cross-multiplying gives x = B × C ÷ A.
Formula: A/B = C/x ⇒ x = B·C/A
Example: A = 3, B = 4, C = 9 → x = 12.
Works for direct proportion; for inverse proportion use x = A × B ÷ C.
Quick steps
- Enter your values — every field shows its unit.
- Press Calculate (or Try an example to see how it works).
- Read the results and copy them if you need them elsewhere.
The calculation runs in your browser. Nothing you type is sent to 1CLIK.
FAQ
How does the Proportion Calculator work?
Cross-multiplying gives x = B × C ÷ A.
What should I keep in mind?
Works for direct proportion; for inverse proportion use x = A × B ÷ C.
Is my data sent anywhere?
No. The numbers stay on your device; the page only shows the result.