Millimeters of water to inches of mercury converter above calculates how many inches of mercury are in 'X' millimeters of water (where 'X' is the number of millimeters of water to convert to inches of mercury). In order to convert a value from millimeters of water to inches of mercury (from mmH2O to inHg) type the number of mmH2O to be converted to inHg and then click on the 'convert' button.