Proportion Calculator
Solve a proportion by entering any three values in A/B = C/D and leaving one field blank. The missing value is calculated using cross multiplication.
Solve proportions
Enter three values and leave exactly one field blank.
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How to use the Proportion Calculator
- Enter three known values in the proportion A/B = C/D.
- Leave exactly one field blank.
- The calculator cross multiplies the known values.
- The missing value and calculation steps are displayed.
Examples
Solve for D
If 5/8 = 15/D, cross multiplication gives D = 24.
Solve for C
If 3/4 = C/20, then C = 15.
Frequently asked questions
What is a proportion?
A proportion states that two ratios or fractions are equal.
How does cross multiplication work?
For A/B = C/D, the cross products are A × D and B × C. In a true proportion those values are equal.
Can I leave any one field blank?
Yes. Leave exactly one value blank and the calculator will solve for that position.
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