Proportion Calculator

Solve a/b = c/d for one unknown using cross multiplication.

Proportion Calculator
Local input
Output
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About this tool

Made for the task at hand.

Find a missing numerator or denominator in an equality of two ratios. The accepted layout is compact and unambiguous.

How to use

  1. Write a/b = c/d with exactly one value replaced by x.
  2. Keep all other entries as finite numbers.
  3. Review x and the equation with the value filled in.
Your work stays yours.
Tool inputs are processed locally in your browser and are never sent to KitVerse servers. Clear the workspace when using a shared device.
Common questions
Can x appear in a denominator?

Yes. Any one of the four positions can be unknown, provided the resulting division is defined.

Can more than one value be unknown?

No. One equation determines one unknown, so the tool requires exactly three known values.