How does cross-multiplication solve a proportion?

For a/b = c/d the cross products are equal, so a × d = b × c. Rearranging gives each unknown — for example the missing d = (b × c) ÷ a. The tool applies whichever rearrangement matches the blank field.

How accurate is the result?

It uses standard double-precision arithmetic rounded to six decimals for display. Results are exact for typical use; the solver reports an error if the rearrangement would divide by zero.

Are my numbers sent anywhere?

No. The solver is privacy-first — everything is computed in your browser and no values are sent to any server.

Proportion Solver (Cross-Multiplication)

Solve a/b = c/d for the missing value by cross-multiplication.

Proportion solver

Solve the proportion a / b = c / d for any one missing term. Enter the three values you know, leave the unknown blank, and the tool finds it by cross-multiplication (a × d = b × c).

It is privacy-first: all of the maths happens locally in your browser, so nothing you type ever leaves your device.