Millimeter of Water (mmH₂O)

The conventional millimetre of water (mmH₂O, also written mmWC or mmAq) is the pressure of a 1 mm column of water of density 1000 kg/m³ under standard gravity: exactly 9.80665 Pa.

Symbol: mmH₂O (ASCII: mmH2O)

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

SI relation: 1 mmH₂O = 9.80665 Pa (exact)

Derivation: 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa

Exact: yes, by definition

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

Typical uses

Fan static pressure and duct design in Asia and Europe
Filter pressure drop (mmAq on Japanese and Korean datasheets)
Low-pressure gas and draught gauges

Convert millimeters of water to other units

1 mmH₂O in other pressure units
Conversion	1 mmH₂O equals	Reverse
millimeter of water to pascal	9.80665 Pa	pascal to millimeter of water
millimeter of water to kilopascal	0.00980665 kPa	kilopascal to millimeter of water
millimeter of water to psi	0.001422334331 psi	psi to millimeter of water
millimeter of water to bar	0.0000980665 bar	bar to millimeter of water
millimeter of water to millimeter of mercury	0.07355591353 mmHg	millimeter of mercury to millimeter of water
millimeter of water to inch of water	0.03937007874 inH₂O	inch of water to millimeter of water
millimeter of water to atmosphere	0.00009678411054 atm	atmosphere to millimeter of water
millimeter of water to megapascal	0.00000980665 MPa	megapascal to millimeter of water
millimeter of water to millibar	0.0980665 mbar	millibar to millimeter of water
millimeter of water to torr	0.07355592401 Torr	torr to millimeter of water
millimeter of water to centimeter of water	0.1 cmH₂O	centimeter of water to millimeter of water
millimeter of water to inch of mercury	0.002895902107 inHg	inch of mercury to millimeter of water
millimeter of water to decibar	0.000980665 dbar	decibar to millimeter of water
millimeter of water to inch of water (60 °F)	0.03940945989 inH₂O (60 °F)	inch of water (60 °F) to millimeter of water
millimeter of water to barye	98.0665 Ba	barye to millimeter 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, "millimeter of water, conventional (mmH2O)".

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). Millimeter of Water (mmH₂O). Retrieved October 17, 2026, from https://scientificconverters.com/units/millimeter-of-water/

IEEE

Scientific Converters, "Millimeter of Water (mmH₂O)," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/millimeter-of-water/