The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units.
millipascals
The millipascal is a multiple of the unit bit for Pressure. The prefix milli (symbol m) is defined in the International System of Units (SI) as a multiplier of 1 × 10-3 (1 thousandth, short scale), and therefore 1 millipascal = 1 × 10-3 pascals = 0.001 pascals. The millipascal has the unit symbol mPa.