# mH2O - Metres of Water Gauge at 4 deg C Pressure Unit

Meters of water gauge or column is a metric unit for measuring liquid level. 1 metre of water column at 4 degrees celsius equals 9806.65 Pascals.

The hydrostatic pressure generated by a certain liquid level is typically represented by the equivalent height of a water column.

Since the pressure exerted by one metre of water is dependent on its density and the local gravity it is not a fundamental unit of measure for pressure but a derived one which is called a manometric unit.

Metres of water column or water gauge are used throughout the world but mostly in Europe to measure the level of fresh water in boreholes, rivers and reservoirs.

Metres of water pressure units are expressed in mostly three different ways which are metres of H2O (mH2O), metres of water gauge (mWG) or metres of water column (mWC).

Since the density of a liquid is affected by changes in temperature, metres of water column should be accompanied by the temperature of the liquid that the units were derived. A pure water density of 1000 kg/m3 at 4 deg C and standard gravity of 9.80665 m/s2 is used in the calculation of this pressure unit. The significance of 4 degrees Celsius (39.2 degrees Fahrenheit) is that it is very close to the temperature that water reaches its maximum density.

It is conventional practice to use 1000 kg/m3 as the density of pure water at 4 deg C which is very close to the precise density and for most measurements this does not introduce any significant error. In fact since the temperature can vary significantly, measuring pressure in metres of water is never going to be a precise representation of the true liquid height. Local gravity also varies at different geological locations, which also adds some minor uncertainties to the use of metres of water gauge as an indication of exact water level in different parts of the world.

Use the conversion factors in the table below to convert from mH2O to other pressure units.

To convert a reading in any pressure unit to mH2O click on the relevant pressure conversion factor below and multiply by the conversion factor for mH2O.

Alternatively convert from a mH2O pressure value into another unit using the pressure unit converter.

Find out how the value for mH2O is determined from SI units or check the different ways of identifying mH2O.

mH2O Pressure Conversion Factors

 0.0980665 bar 1.42229 psi 98.0665 mbar 9806.65 N/m² 9806.65 Pa 98.0665 hPa 9.80665 kPa 0.00980665 MPa 0.1 kg/cm² 1000 mmH2O 4°C (39.2°F) 100 cmH2O 4°C (39.2°F) 1 mH2O 4°C (39.2°F) 39.3701 inH2O 4°C (39.2°F) 3.28084 ftH2O 4°C (39.2°F) 73.5539 mmHg 0°C (32°F) 7.35539 cmHg 0°C (32°F) 2.8959 inHg 0°C (32°F) 73.5559 Torr 73555.9 mTorr 0.0967841 atm 0.1 at 98066.5 dyn/cm² 22.7573 oz/in² 73555.9 µHg 0°C (32°F) 0.000634971 tsi (uk, long) 0.000711167 tsi (usa, short) 0.102408 tsf (usa, short) 204.816 psf 100 g/cm²

Please note that the conversion factors above are accurate to 6 significant figures.

mH2O Derivation
The calculation below shows how the pressure unit Metres of Water Column (mH2O) is derived from SI Units.

Formula

Pressure = Force / Area
Force = Mass x Acceleration
Mass = Density x Volume
Volume = Area x Height
Acceleration = Distance / (Second x Second)

SI Units

Mass: Kilogram (kg)
Length: Metre (m)
Time: Second (s)
Force: Newton (N)
Pressure: Pascal (Pa)

Input Values

Density = Water Density at 4degC = 1000 kg/m³
Area = 1 m²
Height = 1 m
Acceleration = Standard Gravity = 9.80665 m/s²

Calculation

1 mH2O Mass = 1000 kg/m³ x 1 m² x 1 m = 1000 kg
1 mH2O Force = 1000 kg x 9.80665 m/s² = 9806.65 N
1 mH2O Pressure = 9806.65 N / 1 m² = 9806.65 Pa

mH2O Alternate Descriptions

These are the different versions used for identifying mH2O that you may find elsewhere.

Metres of H2O
Meters of H2O
Metres of Water Column
Meters of Water Column
Metres of Water Gauge
Meters of Water Gauge
mH2O
mWC
mWG
mWS
mAq
m H2O
m WC
m WG
m WS
m Aq

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