A centimetre or millimetre of water (US spelling ''centimeter'' or ''millimeter of water'') are less commonly used measures of

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

derived from pressure head.

Centimetre of water

A ''centimetre of water'' (US spelling ''centimeter of water'')NOTE: A centimetre of water is abbreviated as ''cm'' or ''cm H₂O''. is a unit of pressure. It may be defined as the pressure exerted by a column of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

of 1 cm in

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For example, "The height of that building is 50 m" or "The height of an airplane in-flight is ab ...

at 4

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...

(temperature of maximum density) at the

standard acceleration of gravity The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. ...

, so that = × × 1 cm = ≈ , but conventionally a nominal maximum water density of is used, giving . The centimetre of water unit is frequently used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation or in water supply networks (then usually in

metre The metre ( British spelling) or meter ( American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its p ...

s water column). It is also a common unit of pressure in the speech sciences. This unit is commonly used to specify the pressure to which a

CPAP Continuous positive airway pressure (CPAP) is a form of positive airway pressure (PAP) ventilation in which a constant level of pressure greater than atmospheric pressure is continuously applied to the upper respiratory tract of a person. The ...

machine is set after a

polysomnogram Polysomnography (PSG), a type of sleep study, is a multi-parameter study of sleep and a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the ...

. :

Millimetre of water

''Millimetre of water'' (US spelling ''millimeter of water'')NOTE: Millimetre of water is also sometimes addressed as : ''millimetres water column'', abbreviated as ''mmwg'', ''mmH₂O'', or ''mmwc''. is a unit of pressure. It may be defined as the pressure exerted by a column of

of 1 mm in

at 4

(temperature of maximum density) at the

, so that = × × 1 mm = ≈ , but conventionally a nominal maximum water density of is used, giving . : In limited and largely historic contexts it may vary with

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

, using the equation: : ''P'' = ''ρ''·''g''·''h''/1000, : where : ''P'': pressure in Pa : ''ρ'': 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 A raincoat is a waterproof or water-resistant garment worn on the upper body to shield the wearer from rain. The term rain jacket is sometimes used to refer to raincoats with long sleeves that are waist-length. A rain jacket may be combined with ...

or other

outerwear Outerwear is clothing and accessories worn outdoors, or clothing designed to be worn outside other garments, as opposed to underwear. It can be worn for formal or casual occasions, or as warm clothing during winter. List of outerwear * Academic ...

can take or how much water a tent can resist without leaking.

References

{{reflist

External links

Pressure conversion calculator
at

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to ...

website Units of pressure

Centimetre of water

Millimetre of water

See also

References

External links