How it works
For a direct relationship where A maps to B and C maps to X, X = B × C / A. For an inverse relationship, X = A × B / C.
Productivity / HXD Labs
Proportion calculator
Find the fourth value in a proportion using three known numbers.
Result
Fill in the fields to see the result.
How to use
Choose direct proportion when both quantities grow together, or inverse proportion when one falls as the other rises.
Example
If 3 items cost $12, then 5 items cost $20 under a direct proportion.
Good to know
A proportion works only when the relationship remains constant. Fixed fees or volume discounts can invalidate that assumption.