Proportion Calculator
Solve for the unknown variable in any proportion (A/B = C/D) with cross-multiplication steps.
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How to Use the Proportion Calculator
- 1Enter values for A, B, C, and D, leaving the unknown field empty or designated as x.
- 2Choose whether you are solving a direct proportion (A/B = C/D) or an inverse proportion.
- 3The calculator computes x using cross multiplication and displays the step-by-step arithmetic.
- 4Copy your result with one click.
Formula & How It Works
Cross-Multiplication Method
When two ratios are equal (A/B = C/D), their cross-products are equal: A × D = B × C. Solving for any single variable requires dividing the product of the diagonal pair by the remaining known term.
Worked Examples
Direct Proportion Problem
Input: 3 / 8 = 12 / x
Explanation: Cross multiplying gives 3x = 8 × 12 = 96. Dividing both sides by 3 yields x = 32.
Unit Conversion Scale
Input: 1 in / 25.4 mm = 5 in / x mm
Explanation: 1 × x = 25.4 × 5 = 127 mm.
Frequently Asked Questions
How do you check if a proportion is true?▼
A proportion is true if cross-multiplying the two ratios yields identical products (A × D == B × C).
Can I use negative numbers?▼
Yes, our proportion calculator supports positive, negative, and decimal values.
What happens if a denominator is zero?▼
Division by zero is mathematically undefined. The calculator validates inputs and displays a friendly error prompt.
Is this tool suitable for recipe scaling?▼
Yes, it is ideal for scaling ingredients up or down based on serving count.
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