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Proportion Calculator
Solve for the unknown in a proportion a/b = c/d.
Inputs
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Result
Your answer appears here.
Enter values and press Calculate — the result appears here.
How it works
The formula behind this calculator.
a/b = c/d → c = a·d / b
- a, b, c, d
- Four values in a proportion; three known, one unknown
When two ratios are equal, the cross-products are equal. Solve for the unknown by cross-multiplying.
Example: If 3 kg costs $5, how much for 7 kg? 5 × 7 / 3 ≈ $11.67
Ref: Basic algebra
Tips
- 💡 Cross-multiply to solve a/b = c/d for the missing value.
- 💡 Always check your units cancel. If they don't, you set up the ratio wrong.