Proportion Calculator
Solve proportions by finding a missing value. Enter three known values of A/B = C/D.
Enter three values; leave one blank.
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Missing value
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Proportion Formula
A/B = C/D → Cross multiply: A×D = B×C
2/5 = ?/20 → ? = (2 × 20) / 5 = 8
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Last updated: 2026-08-08