Inch of Water (inH₂O)

The conventional inch of water (inH₂O, also written in WC, "WC or in WG) is the pressure of a 1 inch column of water of density 1000 kg/m³ under standard gravity: exactly 249.08891 Pa.

Symbol: inH₂O (ASCII: inH2O)

Quantity: pressure, stress and differential pressure (force per unit area)

SI relation: 1 inH₂O = 249.08891 Pa (exact)

Derivation: 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa

Exact: yes, by definition

Reference conditions. Conventional water column: ρ = 1000 kg/m³ and gₙ = 9.80665 m/s² (≈ water at 4 °C).

History

Water-filled U-tube manometers made inches of water the standard unit for low pressures in US HVAC and gas work. NIST also lists a 60 °F variant (248.84 Pa) that is about 0.1 % smaller.

Typical uses

HVAC total external static pressure (residential ≈ 0.5 inH₂O)
Filter pressure drop (clean ≈ 0.1–0.3, change at ≈ 1.0 inH₂O)
Cleanroom differentials (0.02–0.05 inH₂O)
Gas appliance supply (natural gas ≈ 7 inH₂O, propane ≈ 11 inH₂O)

Convert inches of water to other units

1 inH₂O in other pressure units
Conversion	1 inH₂O equals	Reverse
inch of water to pascal	249.08891 Pa	pascal to inch of water
inch of water to kilopascal	0.24908891 kPa	kilopascal to inch of water
inch of water to psi	0.036127292 psi	psi to inch of water
inch of water to bar	0.0024908891 bar	bar to inch of water
inch of water to millimeter of mercury	1.868320204 mmHg	millimeter of mercury to inch of water
inch of water to atmosphere	0.002458316408 atm	atmosphere to inch of water
inch of water to megapascal	0.00024908891 MPa	megapascal to inch of water
inch of water to millibar	2.4908891 mbar	millibar to inch of water
inch of water to torr	1.86832047 Torr	torr to inch of water
inch of water to millimeter of water	25.4 mmH₂O	millimeter of water to inch of water
inch of water to centimeter of water	2.54 cmH₂O	centimeter of water to inch of water
inch of water to inch of mercury	0.07355591353 inHg	inch of mercury to inch of water
inch of water to decibar	0.024908891 dbar	decibar to inch of water
inch of water to inch of water (60 °F)	1.001000281 inH₂O (60 °F)	inch of water (60 °F) to inch of water
inch of water to barye	2490.8891 Ba	barye to inch of water

Open the Pressure Converter to convert any value between all units.

Sources

Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "inch of water, conventional (inH2O)".

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.

Cite this page

APA

Scientific Converters. (2026, October 15). Inch of Water (inH₂O). Retrieved October 18, 2026, from https://scientificconverters.com/units/inch-of-water/

IEEE

Scientific Converters, "Inch of Water (inH₂O)," scientificconverters.com. Accessed: Oct. 18, 2026. [Online]. Available: https://scientificconverters.com/units/inch-of-water/