Inches of Water Column

Inches of water gauge or column (inWC) is an english and american unit for measuring liquid level. 1 inch of water column at 4 degrees celsius equals 249.089 pascals.

The hydrostatic pressure generated by a certain liquid level is typically represented by the equivalent height of a water column. Since the pressure exerted by one inch of water is dependent on its density and the local gravity it is not a fundamental unit of measure for pressure but a derived one which is called a manometric unit.

Inches of water column or water gauge are used throughout the world for measuring shallow liquid level and low pressures such as differential air pressures in ventilation systems.

Since the density of a liquid is affected by changes in temperature, inches of the water column should be accompanied by the temperature of the liquid that the units were derived from. A pure water density of 1000 kg/m3 at 4 deg C and standard gravity of 9.80665 m/s2 is used in the calculation of this pressure unit. The significance of 4 degrees Celsius (39.2 degrees Fahrenheit) is that it is very close to the temperature that water reaches its maximum density.