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Get NordVPN →Proportion Calculator: Solve a / b = c / x
A free proportion calculator that solves a / b = c / x using cross-multiplication. Enter a, b and c to instantly find the value of x for ratios, scaling and everyday math.
a / b = c / x
Enter a, b and c to find x.
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How it works
What is a proportion?
A proportion states that two ratios are equal, written as a / b = c / x. When one value is unknown, you can solve for it using cross-multiplication.
This calculator finds the missing term x with the formula x = (b × c) / a, so you get an accurate answer without doing the arithmetic by hand.
When to use it
Proportions appear in recipes, map scales, currency conversions, unit pricing and many science problems where quantities grow at the same rate.
Use this tool any time you know three parts of a proportion and need to find the fourth.
Frequently asked questions
›How is x calculated?
By cross-multiplication: x = (b × c) / a.
›Can I use decimals?
Yes, you can enter decimal values for a, b and c.
›What if a is zero?
If a is zero the proportion has no solution, because dividing by zero is undefined.
›Does it work with negative numbers?
Yes, negative values are accepted and handled correctly.
›Is this calculator free?
Yes, it is completely free and works directly in your browser.
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