Centimeters of Water Column is a manometric unit used to relate a pressure reading to the height of fresh water at a temperature of 4 degC. 1 centimeter of water gauge equals 98.0665 pascals.

The cmH2O pressure unit is mostly used to measure breathing on respirators and ventilators which are used in medical and physiological applications such as controlling respiratory conditions or monitoring athletic performance.

There are many ways of writing centimeters of water, but the cause of most confusion are Water Column (WC) and Water Gauge (WG), which both mean exactly the same thing.

For more details on metric water gauge pressure units please see our mWG page.

Please refer to the table below to find the value of 1 cmWC in another pressure unit.

To find the amount of cmWC in a different pressure unit please click on the approriate unit hyperlink in the table below.

Use our website pressure converter to convert multiple values of cmH2o.

Examine how cmH2O is calculated from SI units or check the the different ways of writing mmH2O.

## Conversion Factors

- 0.000980665 bar
- 0.0142233 psi
- 0.980665 mbar
- 98.0665 N/m²
- 98.0665 Pa
- 0.980665 hPa
- 0.0980665 kPa
- 0.0000980665 MPa
- 0.001 kg/cm²
- 10 mmH2O 4°C (39.2°F)
- 1 cmH2O 4°C (39.2°F)
- 0.01 mH2O 4°C (39.2°F)
- 0.393701 inH2O 4°C (39.2°F)
- 0.0328084 ftH2O 4°C (39.2°F)
- 0.735559 mmHg 0°C (32°F)
- 0.0735559 cmHg 0°C (32°F)
- 0.0289590 inHg 0°C (32°F)
- 0.735559 Torr
- 735.559 mTorr
- 0.000967841 atm
- 0.001 at
- 980.665 dyn/cm²
- 0.227573 oz/in²
- 735.559 µHg 0°C (32°F)
- 0.00000634971 tsi (uk, long)
- 0.00000711167 tsi (usa, short)
- 0.00102408 tsf (usa, short)
- 2.04816 psf
- 1 g/cm²

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

## Derivation

The calculation below shows how the pressure unit Centimetres of Water Column (cmH2O) 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 cm = 0.01 m
- Acceleration = Standard Gravity = 9.80665 m/s²

#### Calculation

- 1 cmH2O Mass = 1000 kg/m³ x 1 m² x 0.01 m = 10 kg
- 1 cmH2O Force = 10 kg x 9.80665 m/s² = 98.0665 N
- 1 cmH2O Pressure = 98.0665 N / 1 m² = 98.0665 Pa

## Alternate Descriptions

These are the different versions used for identifying cmH2O that you may find elsewhere.

- Centimetres of H2O
- Centimeters of H2O
- Centimetres of Water Column
- Centimeters of Water Column
- Centimetres of Water Gauge
- Centimeters of Water Gauge
- cmH2O
- cmWC
- cmWG
- cmWS
- cmAq
- cm H2O
- cm WC
- cm WG
- cm WS
- cm Aq
- cmsH2O
- cmsAq
- cms H2O
- cms Aq

## Help

### How does cmH2O differ at 4°C & 20°C

*What is the difference between cmH _{2}O @ 4 deg C and cmH_{2}O @ 20 deg C?*

The difference in pressure relates to the change in density of water between the two temperatures:

- @4degC = 1000 kg/m³
- @20degC = 998.2 kg/m³

Therefore a hydrostatic pressure of 1 cmH2O @20degC = 998.20/1000 cmH_{2}O @4degC = 0.9982 cmH_{2}O @4degC.

### 1.5 cmH2O to bar

*How much pressure in bar do you need to generate a water pressure of 1.50 cmH2O?*

If water is around temperature of 4degC it will be 0.001471bar.

## Glossary of Liquid Level technical terms

- Capacitive Fluid Level Measurement
- Conductive Fluid Level Detection
- Float Fluid Level Detection
- ftH2O – Feet of Water Column at 4 deg C Pressure Unit
- mH2O – Metres of Water Gauge at 4 deg C Pressure Unit
- mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit
- Specific Gravity
- Vibrating Tuning Fork Fluid Level Detection

## Help from Liquid Level resources

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- Determining water tank volume using hydrostatic pressure
- How do you measure the volume of a liquid using pressure
- Calculating required pressure range for fuel tank level measurement