Tool Web

Proportion Calculator

Find the unknown value X in a proportion of the form A : B = C : X. It uses the property A × X = B × C, and all calculations happen inside your browser.

Enter A, B, and C to see X.

How to use

  1. Enter the values A, B, and C in A : B = C : X.
  2. The unknown value X is calculated automatically.
  3. You can also see the completed proportion.

Frequently asked questions

How do I solve for X in a proportion?

In A:B = C:X, the product of the means equals the product of the extremes. So A × X = B × C, which gives X = B × C ÷ A.

Can I enter decimals or fractions?

Yes. You can enter decimals for A, B, and C. A must not be zero to solve for X.

Are the values I enter sent to a server?

No. All calculations happen only inside your browser, and the values you enter are never sent to or stored on any server.