Inches of water to hectopascals conversion calculator above calculates how many hectopascals are in 'X' inches of water (where 'X' is the number of inches of water to convert to hectopascals). In order to convert a value from inches of water to hectopascals (from inH2O to hPa) just type the number of inH2O to be converted to hPa and then click on the 'convert' button.