A traditional unit of pressure. 1 psi equals 144 pounds per square foot (psf), 6.894 75 kilopascals (kPa), 68.9475 millibars (mb), 2.036 inches of mercury (in Hg), 27.7612 inches of water (in WC), or 70.5134 centimeters of water (cm H2O). See below for related notations such as "psig."