Rule of three calculator
Find a missing value in a direct proportion using three known numbers.
Only for direct proportionality, not inverse proportionality. Use consistent units for A and C, and for B and X. Results may be rounded.
Calculations run only in this page’s memory. This tool does not send or save your entries or results.
If A corresponds to B and C corresponds to X, enter A, B and C. A must not be zero; negative numbers are accepted.
How it works
How it works
X = B × C ÷ A. The ratio between corresponding values must remain constant.
Example
If 3 corresponds to 12, then 5 corresponds to 20: 12 × 5 ÷ 3 = 20.
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