what does psi measure
psi â Pounds per Square Inch Pressure Unit Pounds or pound force per square inch (psi, lb/inÂ², pfsi or lbf/inÂ²) is a widely used British and American unit of measure for pressure. 1 psi equals 6,894.76 pascals. In the USA the PSI pressure unit is the pimary unit of measure for pressure and almost all pressure instruments are specified and display in pounds per square inch. The psi is still used extensively in the UK but the bar pressure unit has mostly replaced it as the primary pressure unit.