PSI to Inches of Water Column Conversion Guide
To convert PSI to inches of water column (in WC), multiply PSI by 27.6799. For example, 1 PSI × 27.6799 = 27.68 in WC. To convert in WC back to PSI, divide by 27.6799.
What Is Inches of Water Column (in WC)?
A unit of pressure equal to the pressure exerted by a column of water exactly one inch tall at a standard reference temperature of 68°F (20°C). Used primarily for measuring very low pressures in HVAC systems, natural gas distribution, ductwork, and other applications where PSI would produce impractically small decimal values.
Water column is part of a family of pressure units based on fluid height. The concept is straightforward: the taller the column of liquid, the greater the pressure at its base. A one-inch column of water at standard temperature exerts a pressure of 0.0361 PSI. This makes in WC the preferred unit wherever pressures are measured in fractions of a PSI.
PSI to Inches of Water Column Formula
Converting between PSI and inches of water column uses a fixed factor based on the density of water at standard temperature and standard gravity. For a full explanation of PSI as a pressure unit, see our guide: What Is PSI? Pressure Explained for Industrial & Hydraulic Systems.
Exact factor (at 68°F / 20°C): 1 PSI = 27.6799 in WC | 1 in WC = 0.0361 PSI
Example: 0.5 PSI × 27.6799 = 13.84 in WC | 11 in WC ÷ 27.6799 = 0.397 PSI
PSI to Feet of Head Formula
Feet of head (ft H₂O) is a related unit used in pump engineering and piping system design. It expresses pressure as the height of a water column in feet rather than inches.
Exact factor: 1 PSI = 2.3067 ft H₂O | 1 ft H₂O = 0.4335 PSI
Relationship: ft head = in WC ÷ 12 | in WC = ft head × 12
PSI to Inches of Water Column Reference Chart
The following chart covers the PSI range most commonly encountered in low-pressure applications. Values are calculated at the standard 68°F (20°C) reference temperature.
| PSI | Inches WC (in H₂O) | Feet of Head | Typical Application |
|---|---|---|---|
| 0.036 PSI | 1.0 in WC | 0.083 ft | Gas appliance manifold pressure |
| 0.072 PSI | 2.0 in WC | 0.167 ft | Low-pressure HVAC supply |
| 0.1 PSI | 2.77 in WC | 0.23 ft | HVAC duct static pressure |
| 0.18 PSI | 5.0 in WC | 0.42 ft | Residential gas supply (low) |
| 0.25 PSI | 6.92 in WC | 0.58 ft | Residential gas distribution |
| 0.397 PSI | 11.0 in WC | 0.92 ft | Standard natural gas appliance pressure (NA) |
| 0.5 PSI | 13.84 in WC | 1.15 ft | Low-pressure gas lines |
| 1.0 PSI | 27.68 in WC | 2.31 ft | Low hydraulic / light water systems |
| 2.0 PSI | 55.36 in WC | 4.61 ft | Light irrigation / process water |
| 5.0 PSI | 138.4 in WC | 11.53 ft | Irrigation systems |
| 10 PSI | 276.8 in WC | 23.07 ft | Low-pressure water supply lines |
| 20 PSI | 553.6 in WC | 46.13 ft | Residential water supply (low) |
| 40 PSI | 1,107 in WC | 92.27 ft | Typical residential water pressure |
| 60 PSI | 1,661 in WC | 138.4 ft | Standard municipal water pressure |
| 80 PSI | 2,214 in WC | 184.5 ft | Higher municipal water pressure |
| 100 PSI | 2,768 in WC | 230.7 ft | Industrial water / light hydraulics |
Calculated at 68°F (20°C) reference temperature. Factor: 1 PSI = 27.6799 in WC = 2.3067 ft H₂O. Source: NIST — SI Units and Conversion Factors.
PSI to Feet of Head (ft H₂O)
Feet of head is the preferred pressure unit in pump engineering, irrigation design, and piping system calculations. It expresses pressure as the equivalent height of a water column, which directly relates to how pumps are specified and how piping systems are designed for flow.
Why Feet of Head Matters for Hose and Fluid Systems
When sizing a pump, the total dynamic head (TDH) determines the pump requirement. System pressure in PSI must be converted to feet of head to match pump curves and verify adequate flow at the required pressure. Discharge hoseand suction hose must be rated for the system pressure in PSI, but the pump sizing calculation works in feet of head.
| PSI | Feet of Head | Pump Application Context |
|---|---|---|
| 5 PSI | 11.5 ft | Very low head pump — gravity-assist systems |
| 10 PSI | 23.1 ft | Low head pump — transfer applications |
| 20 PSI | 46.1 ft | Moderate head — residential booster pumps |
| 30 PSI | 69.2 ft | Standard irrigation pump |
| 40 PSI | 92.3 ft | Municipal water delivery |
| 50 PSI | 115.3 ft | Standard municipal water pressure |
| 75 PSI | 173.0 ft | High municipal / industrial water |
| 100 PSI | 230.7 ft | High-pressure water delivery systems |
Factor: 1 PSI = 2.3067 ft H₂O at 68°F. For pump selection and system design, always use the manufacturer pump curve with head in feet.
Where Water Column Pressure Is Used
Inches of water column appears in specifications across several industries that ARG Industrial serves. Understanding where this unit applies helps maintenance technicians and system designers correctly interpret equipment documentation and specify the right products.
Natural Gas & Propane Systems
Natural gas appliance operating pressure in North America is typically specified at 7 in WC (0.25 PSI) for low-pressure supply and 11 in WC (0.40 PSI) for appliance manifold pressure. Gas regulators, flex connectors, and gas hose are rated in in WC or equivalent PSI values. When working with gas systems, always verify the inlet and outlet pressure in the units specified by the equipment manufacturer.
HVAC & Ductwork
HVAC engineers specify duct static pressure, fan performance, and filter pressure drop in inches of water column — typically in the 0.1 to 2.0 in WC range. Air handler units, variable air volume (VAV) boxes, and duct pressure sensors all reference in WC. These are very low pressures — 2.0 in WC is only 0.072 PSI.
Irrigation & Water Systems
Irrigation system designers convert between PSI and feet of head when sizing pumps and calculating zone pressure requirements. Lay-flat discharge hoseand suction hose for irrigation pumps are rated in PSI, while pump specifications reference feet of head. Converting between the two is a routine calculation in system design.
Industrial Process & Instrumentation
Low-pressure process instrumentation, differential pressure gauges, and flow measurement devices frequently use in WC or millimeters of water column (mm WC). Process engineers and instrumentation technicians encounter this unit when working with tank level sensors, orifice plate flow meters, and low-pressure control systems.
Hose & Fitting Selection for Low-Pressure Systems
Low-pressure systems — water supply, irrigation, gas transfer, and HVAC-adjacent applications — require hose and fittings appropriate for their operating pressure and fluid type. While the pressures are low relative to hydraulic systems, selecting correctly rated components is still essential for safety and long service life.
Key Selection Factors for Low-Pressure Hose
- Working pressure:Even at low PSI, verify the hose WP rating exceeds maximum system pressure including surge.
- Fluid compatibility:Water hose, gas hose, and general industrial hose have different inner tube materials. Never use water hose for fuel or chemical transfer.
- Temperature rating:Hot water and steam applications require hose rated for both the pressure and the temperature simultaneously.
- Vacuum rating:Suction hose must be rated for vacuum service. Standard discharge hose will collapse under suction.
- Fitting material:Water and gas service hose fittings are typically brass or stainless steel. Confirm material compatibility with the fluid and environment.
Frequently Asked Questions
Multiply the PSI value by 27.6799to get inches of water column. Example: 2 PSI × 27.6799 = 55.36 in WC. To convert in WC back to PSI, divide by 27.6799.
Inches of water column is a unit of pressure equal to the pressure exerted by a one-inch column of water at 68°F. It is used for very low-pressure measurements in HVAC systems, natural gas lines, ductwork, and instrumentation — applications where PSI values would be impractically small decimals.
1 inch of water column equals 0.0361 PSI(1 ÷ 27.6799). This very low value is why water column is preferred over PSI for gas and HVAC pressure measurements.
11 inches of water column equals approximately 0.397 PSI(11 ÷ 27.6799). 11 in WC is the standard natural gas appliance operating pressure in North America.
Both are units of pressure, but they are used in different ranges. PSI is used for higher-pressure systems like hydraulics, pneumatics, and pressurized water. Inches of water column is used for very low-pressure systems like gas lines and HVAC where PSI values would be small, hard-to-work-with decimals. 1 PSI equals 27.68 in WC.
Multiply PSI by 2.3067to get feet of head. Example: 10 PSI × 2.3067 = 23.07 feet of head. To convert feet of head to PSI, divide by 2.3067. Feet of head is used in pump engineering and irrigation design.
Feet of head and inches of water column measure the same thing — the height of a water column — just in different units. To convert: ft head = in WC ÷ 12and in WC = ft head × 12. Both convert to PSI using the same water density factor.