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Math

Proportion Calculator

Solve for x in the positive proportion a/b = c/x.

Exact method explained belowEditable inputs

Set up your calculation

Runs on your device

SOLUTION

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter a, b, c.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Cross-multiply a × x = b × c, then divide by a: x = b × c ÷ a.

A WORKED EXAMPLE

For 2/3 = 10/x, x is 15. Both sides equal two-thirds.

What to keep in mind

All three inputs must be positive. This assumes direct proportionality and does not establish that real-world quantities scale linearly.

Common questions

Where is the missing value?

It is the denominator of the second fraction: c/x. Rearrange your known values accordingly.

Can this scale a recipe?

Yes, when ingredient quantities scale directly. Cooking time or temperature may not scale in the same way.

Methodology maintained by ClarityKit. How these tools are built and checked.