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mmH2O - Millimetres of Water Column at 4 deg C Pressure Unit

Millimeters of Water Column is a low range metric pressure unit derived from the hydrostatic pressure of 1mm head of water at 4 degC. 1 Millimeter of Water Gauge equals 9.80665 Pascals.

The mmH2O pressure unit is used for monitoring low air flow pressures used in building ventilation systems or very low water levels in rivers and streams. Historically low air pressures were measured using water column manometers but although these instruments have been mostly replaced by digital manometers which use electronic sensors, the mmH2O pressure unit remains in use.

For more background information on metric water column pressure units please go to our mH2O page.

To find the equivalent pressure value of 1 mmWC in other units please use the list below.

Click on the applicable unit below to obtain the conversion factor for converting into Millimetres of Water Column.

Use the site pressure converter to calculate many different readings in mmWG.

Go to the section which shows how mmH2O is derived from SI units or verify the list of the description variations for mmH2O.



mmH2O Pressure Conversion Factors
0.0000980665bar
0.00142233psi
0.0980665mbar
9.80665N/m²
9.80665Pa
0.0980665hPa
0.00980665kPa
0.00000980665MPa
0.0001kg/cm²
1mmH2O 4°C (39.2°F)
0.1cmH2O 4°C (39.2°F)
0.001mH2O 4°C (39.2°F)
0.0393701inH2O 4°C (39.2°F)
0.00328084ftH2O 4°C (39.2°F)
0.0735559mmHg 0°C (32°F)
0.00735559cmHg 0°C (32°F)
0.00289590inHg 0°C (32°F)
0.0735559Torr
73.5559mTorr
0.0000967841atm
0.0001at
98.0665dyn/cm²
0.0227573oz/in²
73.5559µHg 0°C (32°F)
0.000000634971tsi (uk, long)
0.000000711167tsi (usa, short)
0.000102408tsf (usa, short)
0.204816psf
0.1g/cm²

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

mmH2O Derivation
The calculation below shows how the pressure unit Millimetres of Water Column (mmH2O) 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 mm = 0.001 m
Acceleration = Standard Gravity = 9.80665 m/s²



Calculation

1 mmH2O Mass = 1000 kg/m³ x 1 m² x 0.001 m = 1 kg
1 mmH2O Force = 1 kg x 9.80665 m/s² = 9.80665 N
1 mmH2O Pressure = 9.80665 N / 1 m² = 9.80665 Pa

mmH2O Alternate Descriptions

These are the different versions used for identifying mmH2O that you may find elsewhere.

Millimetres of H2O
Millimeters of H2O
Millimetres of Water Column
Millimeters of Water Column
Millimetres of Water Gauge
Millimeters of Water Gauge
mmH2O
mmWC
mmWG
mmWS
mmAq
mm H2O
mm WC
mm WG
mm WS
mm Aq

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Site Last Updated:  09/02/12

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