Foot of Water Column is an American and English low value pressure unit, now used mostly in the USA where feet and inches are the standard units for measuring distance. 1 foot of water column at 4 degC (39.2 degF) equals 2989.07 pascals.
The main use for the feet of water pressure unit is to measure fluid level in a tank or depth in a liquid such as sea water. Water is the most common liquid found on Earth and the density of all other types of liquid are referenced and compared to the density of water. If the specific gravity (ratio of density comparison with water) of a certain liquid is known, it will be possible to convert the required height range into feet of water to make it possible to select the correct hydrostatic range for a liquid level measurement device.
For more background information on American and British hydrostatic pressure units please go to our inches of water page.
You will find various conversion factors for 1 foot of water gauge in the list below.
To convert other pressure units into feet of water column please click on the appropriate link in the table below.
Calculate any number of ftWG values using our online pressure converter.
View the calculation for deriving ftH2O from SI units or the list of different forms of writing ftH2O that you might see used.
Conversion Factors
- 0.0298907 bar
- 0.433528 psi
- 29.8907 mbar
- 2989.07 N/m²
- 2989.07 Pa
- 29.8907 hPa
- 2.98907 kPa
- 0.00298907 MPa
- 0.0304800 kg/cm²
- 304.800 mmH2O 4°C (39.2°F)
- 30.4800 cmH2O 4°C (39.2°F)
- 0.304800 mH2O 4°C (39.2°F)
- 12 inH2O 4°C (39.2°F)
- 1 ftH2O 4°C (39.2°F)
- 22.4198 mmHg 0°C (32°F)
- 2.24198 cmHg 0°C (32°F)
- 0.882671 inHg 0°C (32°F)
- 22.4198 Torr
- 22419.8 mTorr
- 0.0294998 atm
- 0.0304800 at
- 29890.7 dyn/cm²
- 6.93644 oz/in²
- 22419.8 µHg 0°C (32°F)
- 0.000193539 tsi (uk, long)
- 0.000216764 tsi (usa, short)
- 0.0312140 tsf (usa, short)
- 62.4280 psf
- 30.4800 g/cm²
Please note that the conversion factors above are accurate to 6 significant figures.
Derivation
The calculation below shows how the pressure unit Feet of Water Column (ftH2O) is derived from SI Units.
Formula
- Pressure = Force / Area
- Force = Mass x Acceleration
- Mass = Density x Volume
- Volume = Area x Height
- Acceleration = Distance / (Time x Time)
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 ft = 0.3048 m
- Acceleration = Standard Gravity = 9.80665 m/s²
Calculation
- 1 ftH2O Mass = 1000 kg/m³ x 1 m² x 0.3048 m = 304.8 kg
- 1 ftH2O Force = 304.8 kg x 9.80665 m/s² = 2989.06692 N
- 1 ftH2O Pressure = 2989.06692 N / 1 m² = 2989.0992 Pa
Alternate Descriptions
These are the different versions used for identifying inH2O that you may find elsewhere.
- Feet of H2O
- Foot of H2O
- Feet of Water Column
- Foot of Water Column
- Feet of Water Gauge
- Foot of Water Gauge
- ftH2O
- ftWC
- ftWG
- ftWS
- ftAq
- ft H2O
- ft WC
- ft WG
- ft WS
- ft Aq
- ‘H2O
- ‘WC
- ‘WG
- ‘WS
- ‘Aq
Conversion Tables
Select a look up table for converting a pressure reading in feet of water column to other measurement units.
Glossary of Liquid Level technical terms
- Capacitive Fluid Level Measurement
- cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit
- Conductive Fluid Level Detection
- Float Fluid Level Detection
- Hydrostatic Pressure
- 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
- Measuring liquid level in a sealed tank with a hydrostatic pressure sensor
- Measuring the volume of liquid in a horizontal cylinder tank
- 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
- Measuring liquid level in a tank using a dp sensor
