**Inches of water gauge or column is an english and american unit for measuring liquid level. 1 inch of water column at 4 degrees celsius equals 249.089 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 inch 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.

Inches of water column or water gauge are used throughout the world for measuring shallow liquid level and low pressures such as differential air pressures in ventilation systems.

Since the density of a liquid is affected by changes in temperature, inches 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 practise 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 inches 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 inches of water gauge as an indication of exact water level in different parts of the world.

Use the conversion factors below to convert from inH2O to other pressure units or vice versa. To convert a reading in inH2O to another unit multiply it by the relevant pressure conversion factor. To convert a reading in any pressure unit to inH2O divide it by the relevant pressure conversion factor.

Alternatively convert from inH2O into another unit using the inches of water converter table or the pressure unit converter.

See how inH2O are derived from SI units or check other forms for describing inH2O.

inH2O Pressure Conversion Factors

0.00249089 | bar |

0.0361273 | psi |

2.49089 | mbar |

249.089 | N/m² |

249.089 | Pa |

2.49089 | hPa |

0.249089 | kPa |

0.000249089 | MPa |

0.00254000 | kg/cm² |

25.4 | mmH2O 4°C (39.2°F) |

2.54 | cmH2O 4°C (39.2°F) |

0.0254 | mH2O 4°C (39.2°F) |

1 | inH2O 4°C (39.2°F) |

0.0833333 | ftH2O 4°C (39.2°F) |

1.86832 | mmHg 0°C (32°F) |

0.186832 | cmHg 0°C (32°F) |

0.0735559 | inHg 0°C (32°F) |

1.86832 | Torr |

1868.32 | mTorr |

0.00245832 | atm |

0.00254000 | at |

2490.89 | dyn/cm² |

0.578037 | oz/in² |

1868.32 | µHg 0°C (32°F) |

0.0000161283 | tsi (uk, long) |

0.0000180636 | tsi (usa, short) |

0.00260117 | tsf (usa, short) |

5.20233 | psf |

2.54 | g/cm² |

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

inH2O Derivation

The calculation below shows how the pressure unit Inches of Water Column (inH2O) 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 in = 0.0254 m

Acceleration = Standard Gravity = 9.80665 m/s²

**Calculation**

1 inH2O Mass = 1000 kg/m³ x 1 m² x 0.0254 m = 25.4 kg

1 inH2O Force = 25.4 kg x 9.80665 m/s² = 249.08891 N

1 inH2O Pressure = 249.08891 N / 1 m² = 249.08891 Pa

inH2O Alternate Descriptions

These are the different versions used for identifying inH2O that you may find elsewhere.

Inches of H2O

Inch of H2O

Inches of Water Column

Inch of Water Column

Inches of Water Gauge

Inch of Water Gauge

inH2O

inWC

inWG

inWS

inAq

in H2O

in WC

in WG

in WS

in Aq

"H2O

"WC

"WG

"WS

"Aq

enquiries@sensorsone.co.uk

Products

- Instrument Type
- 4-20mA Transmitters
- 0-5, 10V Transducers
- mV/V Sensors
- Digital Sensors
- Absolute Sensors
- ATEX Transmitters
- Calibration Pumps
- Calibrators
- Compound Ranges
- Data Loggers
- Digital Gauges
- Digital Manometers
- Digital Readouts
- DP Transmitters
- Indicators - Pressure
- Liquid Level Sensors
- Suction Pressure Sensors
- Switches
- Accessories
- Your Application
- Absolute Reference
- Air/Pneumatics
- Barometric/Atmospheric
- Certificates & Approvals
- Data Logging
- Differential
- Flush Diaphragm
- Gauge Reference
- High Accuracy
- High Frequency Response
- High Range
- High Temperature
- Intrinsically Safe
- Leak Testing
- Level Measurement
- Low Ranges
- Measurement Signal
- Measuring Range
- Media Compatibility
- Miniature
- OEM Design
- Overpressure Protection
- PC Interfacing
- Pressure Calibration
- Process Connection
- Testing
- Sensor Technology
- Submersible
- Temperature & Pressure
- Vacuum
- Water Level
- Water Pressure
- Manufacturers

tel: +44 (0)844 800 9885

Tools

Reference

Specify

- Product Finder - Choose multiple product and application types to filter out a suitable product
- Pressure Sensor Specifier - Select parameters to generate a pressure transducer or transmitter specification for your own use or to submit as an enquiry
- Digital Indicator Specifier - Select options for creating a specification for a digital indicator or digital controller for your own use or to submit as an enquiry

Articles

- Measuring vacuum pressure with negative gauge or absolute pressure ranges

» view article - What is the difference between a pressure transducer and a transmitter

» view article - What is the difference between gauge and absolute pressure measurement

» view article - What to consider when selecting a differential pressure sensor

» view article - What affects the performance of low pressure sensors

» view article - Supply voltage and load resistance considerations for pressure transmitters

» view article - Measuring liquid level in a sealed tank with a hydrostatic pressure sensor

» view article - Interpreting specifications of pressure sensor accuracy

» view article

©2015 SensorsONE Ltd, all rights reserved.