Solve a proportion A:B = C:D for the missing value.
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Understanding your result
Leave one and only one field empty so the tool knows what to solve for.
Formula and method
In a proportion A:B = C:D, the cross products are equal: A × D = B × C. The missing value is found by rearranging.
Worked example
1:2 = 5:? solves to 10, because 1 × ? = 2 × 5.
How to use this tool
- Fill in three of the four values.
- Leave the unknown blank.
- Press Solve.
Common mistakes to avoid
- Leaving more than one field blank.
About the Ratio Calculator
Solve a proportion of the form A:B = C:D by leaving exactly one field blank.
Frequently asked questions
Can it simplify a ratio?
Yes. Enter just A and B to see the simplified ratio.