Solve proportions of the form A/B = C/D for any one missing value using cross-multiplication, or check whether two ratios are equal.
About this tool
Solve proportions for the missing value and check whether two ratios are equal.
How to use Proportion Calculator
- Fill in three of A, B, C and D.
- Leave the unknown one empty.
- Read the answer and the cross-multiplication rule used.
Worked example
If 2 kg of apples cost 5 and you want 8 kg, enter A = 2, B = 5, C = 8 and leave D empty: D = 20.
What is cross-multiplication?
In A/B = C/D, A × D equals B × C, so any one value can be found from the other three.
How do I check two ratios?
Fill in all four values; the tool says whether A × D equals B × C.
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