Pounds per square inch to millipascals conversion calculator above calculates how many millipascals are in 'X' pounds per square inch (where 'X' is the number of pounds per square inch to convert to millipascals). In order to convert a value from pounds per square inch to millipascals (from psi to mPa) just type the number of psi to be converted to mPa and then click on the 'convert' button.