PSI to Inches of Water Converter
Convert psi to inches of water column (in H2O, also written in w.c. or inWC). Multiply psi by 27.68. Low pressures such as gas supply and duct static pressure are given in inches of water because the psi figures are awkwardly small.
Enter a value to convert
Free download
Get the printable pipe flow chart
Schedule 40 pipe sizes, water flow in GPM and LPM at four design velocities, and recommended velocities by application. One PDF, made to pin above the bench.
How It Works
An inch of water column is the pressure under a column of water one inch high. It is what a U-tube manometer reads, and it is how gas appliance inlet pressures, gas regulator outlets and duct static pressures are specified in North America. At 27.6799 inches per psi, a 0.25 psi gas line is 6.92 in w.c.
The unit is defined in water, so no specific gravity applies: a gas pressure of 7 in w.c. means the pressure that would hold up 7 inches of water, whatever the gas.
Formula
in H2O = psi × 27.6799
This uses the conventional inch of water, 249.089 Pa (1,000 kg/m³ under standard gravity). References based on water at 60 °F give 27.7076 in per psi, a difference of 0.1%.
Worked Example
A gas line runs at 0.5 psi:
0.5 × 27.6799 = 13.84 in w.c.
PSI to Inches of Water Table
| psi | in H2O | mbar |
|---|---|---|
| 0.05 psi | 1.384 in H2O | 3.44738 mbar |
| 0.1 psi | 2.76799 in H2O | 6.89476 mbar |
| 0.2 psi | 5.53598 in H2O | 13.7895 mbar |
| 0.25 psi | 6.91998 in H2O | 17.2369 mbar |
| 0.3 psi | 8.30397 in H2O | 20.6843 mbar |
| 0.4 psi | 11.072 in H2O | 27.579 mbar |
| 0.5 psi | 13.84 in H2O | 34.4738 mbar |
| 0.75 psi | 20.7599 in H2O | 51.7107 mbar |
| 1 psi | 27.6799 in H2O | 68.9476 mbar |
| 2 psi | 55.3598 in H2O | 137.895 mbar |
| 5 psi | 138.4 in H2O | 344.738 mbar |
Going the other way? Use the inches of water to psi converter. To size a gas line, use the gas flow calculator.
FAQ
Common questions about converting psi to inches of water.
Frequently Asked Questions
How do I convert psi to inches of water?
Multiply psi by 27.6799. For example, 0.5 psi × 27.6799 = 13.84 in w.c.
How many inches of water is 1 psi?
27.6799 in H2O on the conventional basis. 27.7 is the usual rounded figure.
What does in w.c. mean?
Inches of water column. It is the same unit as in H2O and inWC: the pressure under one inch of water, 249.089 Pa.
Why is gas pressure measured in inches of water?
Low-pressure gas supply to appliances runs at a fraction of a psi, so inches of water give workable numbers. Natural gas appliances in North America are typically supplied at around 7 in w.c. and propane at around 11 in w.c., which are about 0.25 psi and 0.4 psi.
How do I convert inches of water to mbar?
Multiply by 2.49089. For example, 8 in w.c. is 19.9 mbar, and the nominal 21 mbar UK natural gas supply is 8.43 in w.c.
Embed This Calculator
Add this free calculator to your website. Copy the code below and paste it into your page.
Related Calculators
Continue your analysis with these related engineering tools
Professional hydraulic engineering calculators for engineers, technicians, and students.
Main Tools
Advanced Tools
- Reynolds Number Calculator
- Head Loss Calculator
- Pump Power Calculator
- Total Dynamic Head Calculator
- Tank Fill/Drain Calculator
- Orifice Plate Calculator
- Weir Flow Calculator
- Manning's Equation Calculator
- Valve Cv Calculator
- Gas Flow Calculator
- Mass Flow Rate Calculator
- Pump Affinity Laws Calculator
- Heat Exchanger Calculator
- Tankless Water Heater Calculator
- Economic Pipe Diameter Calculator
Engineering Guides
Company & Resources
Related Tools
- Electrical Calculators Motor, cable and voltage drop calculators
- Heating Planner UK heat loss, radiator and heat pump calculators
- Solar Sizing Calculator Solar, battery and off-grid sizing calculators
© 2026 Flow Rate Calculator. All rights reserved. A Nomogram Works site.