Proportion Calculator
Solve for the missing value in a proportion. Enter any three values and the fourth is calculated instantly.
Enter any 3 values to solve for the 4th:
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Missing Value
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Solved Variable
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Proportion
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Cross-Multiply Check
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How to Use the Proportion Calculator
- Fill in three values: Enter numbers in any three of the four fields (A, B, C, D).
- Leave one empty: The empty field is the unknown value.
- View the result: The missing value and the complete proportion appear instantly.
Cross-Multiplication Method
A proportion states that two ratios are equal: A/B = C/D. Using cross-multiplication:
- A × D = B × C
- Solve for A: A = (B × C) / D
- Solve for B: B = (A × D) / C
- Solve for C: C = (A × D) / B
- Solve for D: D = (B × C) / A
Frequently Asked Questions
What is a proportion?
A proportion is an equation that states two ratios are equal. For example, 1/2 = 3/6 is a proportion because both ratios equal 0.5.
What is cross-multiplication?
Cross-multiplication is a shortcut for solving proportions. In A/B = C/D, multiply diagonally: A × D = B × C. Then solve for the unknown variable.
Can I use decimals?
Yes, you can use any decimal values. The calculator handles fractional inputs and provides precise results.