Proportion Calculator
Solve proportions of the form A/B = C/D by entering any three values and leaving one blank.
Proportion Calculator
Solve proportions of the form A/B = C/D by entering any three values and leaving one blank.
How to use the Proportion Calculator
- Enter three of the four values (A, B, C, D).
- Leave exactly one field blank for the calculator to solve.
- Click Calculate.
Formula
A/B = C/D
Solving for D: D = BC/A
Solving for A: A = BD/C
Example
If 3/8 = x/40, then x = 3×40/8 = 15.
Step-by-step calculation
- Cross-multiply: 3 × 40 = 120.
- Divide by the remaining denominator: 120 ÷ 8 = 15.
- Answer: x = 15.
Real-world uses
- Scaling recipes up or down.
- Unit conversion ratios.
- Map scale calculations.
- Recipe and mixture scaling.
Common mistakes
- Leaving more than one field blank.
- Placing the unknown in the wrong position.
- Using zero in a denominator position.
Frequently asked questions
Can I enter all four values?
Yes. The calculator will verify whether the proportion holds true.
What does "cross multiplication" mean?
Multiply A×D and B×C. If the proportion is correct, both products are equal.
Can I use negative numbers?
Yes, but be aware that negative ratios in proportions may not represent real-world scenarios.