Do I need to sign up?

No. The tool works without an account.

Are my data uploaded?

Compatible operations run locally in the browser.

Cross-multiply: a/b = c/x → a·x = b·c → x = (b·c)/a. The tool solves for the empty field.

Enter exactly three numbers and leave one blank so the calculator knows which value to solve for.

Tool guide

Practical information to understand the result and use this tool correctly.

Solve proportions: find the missing value in a:b = c:x or scale ratios quickly in the browser.

The tool runs directly in the browser for immediate results.

Do I need to sign up?: No. The tool works without an account.
Are my data uploaded?: Compatible operations run locally in the browser.
How does the proportion formula work?: Cross-multiply: a/b = c/x → a·x = b·c → x = (b·c)/a. The tool solves for the empty field.
What if I leave more than one field empty?: Enter exactly three numbers and leave one blank so the calculator knows which value to solve for.