Pounds per square foot
Pounds per square foot (psf) is a unit used in the United States, United Kingdom and some other countries that use the Imperial system. It is the pressure of a one pound on an area of one square foot.
pound force per square inch
Pound force per square inch (psi) is a unit from the Imperial system defined as the pressure resulting from a force of one pound-force applied to an area of one square inch. It is used in various applications such as tire pressure and hydraulic systems.