Proportion Calculator.
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Browse allWhat Is a Proportion Calculator?
A proportion states that two ratios are equal — like 3/4 = 6/8. This free proportion calculator uses cross-multiplication to find any missing numerator or denominator in a/b = c/d, and shows both ratios as decimals and percentages.
How to Use This Calculator
- Select which value is unknown (a, b, c, or d).
- Enter the three known values in the proportion fields.
- Read the solved value and ratio comparison in the results panel.
- Check the percentage equivalent for the left ratio.
Proportion Formula
- a, c = numerators (top values)
- b, d = denominators (bottom values)
- To solve for d: d = (b × c) / a
Worked Example
Solve 3/4 = 6/d. Cross-multiply: 3 × d = 4 × 6, so 3d = 24, and d = 8. Check: 3/4 = 0.75 and 6/8 = 0.75 — the proportion holds.
Common Use Cases
- Scaling recipe ingredients up or down
- Converting map distances to real-world measurements
- Solving algebra homework with missing numerators or denominators
Frequently Asked Questions (FAQs)
How do you solve a proportion?
For a/b = c/d, cross-multiply: a × d = b × c. Then isolate the unknown. If x/b = c/d, then x = (b × c) / d.
What is the difference between a ratio and a proportion?
A ratio compares two quantities (like 3:4). A proportion states that two ratios are equal (like 3/4 = 6/8).
Can this calculator find any missing value?
Yes. Choose which of a, b, c, or d is unknown and enter the other three — the tool solves via cross-multiplication.
What is cross-multiplication?
Cross-multiplication sets a × d equal to b × c. In a true proportion, both products are identical.
How do you solve 3/4 = x/8?
Cross-multiply: 3 × 8 = 4 × x, so 24 = 4x, and x = 6. The proportion 3/4 = 6/8 is correct.
What happens if a denominator is zero?
Division by zero is undefined. The calculator shows an error instead of returning a result when a denominator would be zero.