square inch to square millimeter Converter

To convert square inch to square millimeter, multiply the value in square inch by 645.16.

For example, 1 square inch = 645.16 square millimeter.

In reverse, 1 square millimeter = 0.00155 square inch.

To convert square inch to square millimeter, enter your value in square inch into the converter above. The tool automatically applies the correct conversion ratio and shows the result in square millimeter.

This page is useful when you need a fast answer, a quick reference table, or the exact formula for switching between square inch and square millimeter.