Millimeters, water gauge, also known as a millimetre of water (US spelling millimeter of water) or millimetres water column and abbreviated to mmwg, mmH2O or mmwc, respectively, is a less commonly used unit of pressure. It may be defined as the pressure exerted by a column of water of 1 mm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity, so that 1 mmH2O (4°C) = 999.9720 kg/m3 × 9.80665 m/s2 × 1 mm = 9.8063754138 Pa ≈ 9.80638 Pa, but conventionally a nominal maximum water density of 1000 kg/m³ is used, giving 9.80665 Pa.
In limited and largely historic contexts it may vary with temperature, using the equation:
- P = Ï·g·h/1000
- where
- P: pressure in Pa
- Ï: density of water (conventionally 1000 kg/m3 at 4°C)
- g: acceleration due to gravity (conventionally 9.80665 m/s2 but sometimes locally determined)
- h: water height in millimetres
The unit is often used to describe how much water rainwear or other outerwear can take or how much water a tent can resist without leaking.
See also
What is WATER COLUMN? What does WATER COLUMN mean? WATER COLUMN meaning & explanation - What is WATER COLUMN? What does WATER COLUMN mean? WATER COLUMN meaning - WATER COLUMN definition - WATER COLUMN explanation.
- Centimetre of water
- ^ nist.gov â€" Guide for the Use of the International System of Units (SI) page 47, 2008 Edition
