The psi, or pounds per square inch, is a unit of pressure (P) using the foot-pound-second (FPS) system. To calculate psi, divide the force applied (F) with the area (A).

**Measure the force applied**Use an instrument such as a force gauge, spring scale or strain gauge. Make sure that the unit is in pounds. Convert the value if necessary.

**Measure the total area on which force is applied**Measure the length and the width, and make sure that both values use the same unit, in this case inches, you can proceed to multiply them.

**Calculate the pressure in psi**Divide the measured force (in pounds) with the measure area (in square inches).