PSI to Inches of Water Converter

How to Convert PSI to Inches of Water

Inches of water column (inH2O or in WC) is a pressure unit commonly used in HVAC, ventilation, and low-pressure measurement. It represents the height of a water column that would produce the same pressure. Manometers and differential pressure gauges in ductwork often read in inches of water because the values are easy to interpret at the low pressures typical of air systems.

One psi equals approximately 27.7076 inches of water. This conversion is essential when calibrating HVAC instruments, reading fan static pressure, or comparing US pressure units with metric equivalents.

For related conversions, try our Pressure Converter, PSI to ATM Converter, or kPa to PSI Converter.

The Conversion Formula

To convert PSI to inches of water:

$$\text{inH}_2\text{O} = \text{PSI} \times 27.7076$$

To convert inches of water to PSI:

$$\text{PSI} = \frac{\text{inH}_2\text{O}}{27.7076}$$

For example, 1 psi equals 27.71 inches of water, and 8 psi equals approximately 221.66 inches of water (about 18.5 feet of water column).

Common PSI to Inches of Water Values

• 0.036 psi = 1 inH2O (typical duct static pressure)
• 0.5 psi = 13.85 inH2O
• 1 psi = 27.71 inH2O
• 5 psi = 138.54 inH2O
• 8 psi = 221.66 inH2O

Where Inches of Water Is Used

HVAC technicians use inches of water to measure duct static pressure, fan total pressure, and filter pressure drop. Values are typically between 0.1 and 2 inH2O for residential systems. Gas pressure regulators and natural gas piping also reference inches of water column for low-pressure delivery (typically 7 to 14 inH2O for household gas).

Water column pressure is intuitive: 1 inH2O is the pressure at the bottom of a 1-inch tall column of water. A manometer filled with water directly shows this height.