Millimeters of water to kilopascals conversion calculator above calculates how many kilopascals are in 'X' millimeters of water (where 'X' is the number of millimeters of water to convert to kilopascals). In order to convert a value from millimeters of water to kilopascals (from mmH2O to kPa) just type the number of mmH2O to be converted to kPa and then click on the 'convert' button.