Millimetres of Water Column (mmWC)

Millimeters of Water Column is a low range metric pressure unit derived from the hydrostatic pressure of 1mm head of water at 4 degC. 1 millimeter of water gauge equals 9.80665 pascals.

The mmH2O pressure unit is used for monitoring low air flow pressures used in building ventilation systems or very low water levels in rivers and streams. Historically low air pressures were measured using water column manometers but although these instruments have been mostly replaced by digital manometers which use electronic sensors, the mmH2O pressure unit remains in use.