Proportion Calculator
Solve proportions for the missing value and check whether two ratios are equal.
Enter your values to see the result.
Solves A / B = C / D. Leave exactly one box empty to find it, or fill all four to check whether the ratios are equal.
Continue your work
- Ratio Calculator — Simplify or scale ratios.
- Percentage Calculator — Solve percentage problems.
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Clear instructions
Find steps, examples and limitations below.
Use online
Open the tool in a supported web browser.
Free to use
No sign-up required. Tool-specific limits may apply.
How to use the Proportion Calculator
Solve proportions for the missing value and check whether two ratios are equal.
- 1 Fill in three of A, B, C and D.
- 2 Leave the unknown one empty.
- 3 Read the answer and the cross-multiplication rule used.
Example and practical tips
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.
Frequently asked questions
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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