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Multiple conversions
To convert from meter of water @ 4°C (mH2O) to pascal (Pa), use the following formula:
pascal (Pa)
= 9.80665 × 1000× meter of water @ 4°C (mH2O)
= 9806.65× meter of water @ 4°C (mH2O)
To convert a pressure from meters of water column (mH₂O) to kilopascals (kPa), multiply by 9.80665.
The factor is standard gravity itself: a one-meter column of water (density 1,000 kg/m³) under g = 9.80665 m/s² exerts exactly 9.80665 kPa at its base. The everyday shortcut "1 m ≈ 10 kPa" overstates pressure by about 2%.
A rainwater tank stands on a hill with its water surface 15 m above a garden tap, and you want the static pressure at the tap in kPa:
That is enough for garden irrigation but well below the 250–350 kPa a typical mains-pressure appliance expects — the calculation that decides whether a gravity-fed system needs a pressure pump.
| mH₂O | kPa |
|---|---|
| 1 | 9.81 |
| 5 | 49.03 |
| 10 | 98.07 |
| 15 | 147.10 |
| 25 | 245.17 |
| 50 | 490.33 |
This conversion is a fixture of plumbing practice in kPa countries — Australia and New Zealand above all, where AS/NZS 3500 expresses supply requirements in kPa (e.g. the widely cited 500 kPa maximum static pressure at a dwelling outlet) while tank stands, bores and pump lifts are naturally discussed in meters of head. It appears equally in pump engineering, where manufacturers publish head in meters but system specifications, NPSH margins and instrument readings may be in kPa, and in geotechnics, where pore-water pressures measured by piezometers convert between water-column height and kPa for stability calculations. One assumption to keep visible: the factor 9.80665 is for clean, cold water. Hot water, seawater or liquids with other densities change the relationship in proportion to specific gravity — a meter of seawater is about 10.06 kPa, and a meter of gasoline only about 7.2 kPa.
To convert from meter of water @ 4°C (mH2O) to megapascal (MPa), use the following formula:
megapascal (MPa)
= 9.80665 × 11000× meter of water @ 4°C (mH2O)
= 0.00980665× meter of water @ 4°C (mH2O)
To convert from meter of water @ 4°C (mH2O) to hectopascal (hPa), use the following formula:
hectopascal (hPa)
= 9.80665 × 10× meter of water @ 4°C (mH2O)
= 98.0665× meter of water @ 4°C (mH2O)
To convert from meter of water @ 4°C (mH2O) to millibar (mbar), use the following formula:
millibar (mbar)
= 9.80665 × 10× meter of water @ 4°C (mH2O)
= 98.0665× meter of water @ 4°C (mH2O)
To convert pressure from meters of water column (mH2O) to bar, multiply by 0.0980665.
The number is not arbitrary: one meter of water column is the hydrostatic pressure exerted by a 1 m tall column of water under standard gravity (9.80665 m/s²) at the conventional reference density of 1,000 kg/m³. That works out to 9,806.65 Pa, and dividing by 100,000 Pa per bar gives 0.0980665.
The most useful anchor to memorize is the reverse one:
A borehole pump must lift water 85 m to the surface tank (its static head). The pressure this represents at the pump outlet:
Reverse direction: a pressure sensor reading 2.5 bar at the bottom of a tank corresponds to 2.5 ÷ 0.0980665 ≈ 25.49 m of water above it.
| mH2O | bar |
|---|---|
| 1 | 0.0981 |
| 5 | 0.4903 |
| 10 | 0.9807 |
| 10.197 | 1.0000 |
| 25 | 2.4517 |
| 50 | 4.9033 |
| 100 | 9.8067 |
Centrifugal pump curves are published in meters of head because head is independent of fluid density — the same impeller lifts any liquid the same height. But pipework components, pressure switches, safety valves and transmitters are all rated in bar. Converting between the two is therefore daily business in pump sizing, sprinkler design and well engineering. One caution: the 0.0980665 factor assumes cold water. For hot water (lower density) or other liquids, multiply by the fluid's specific gravity — 60 m of head in brine at SG 1.2 is 60 × 0.0980665 × 1.2 ≈ 7.06 bar, not 5.88 bar.
To convert from meter of water @ 4°C (mH2O) to torr (torr), use the following formula:
torr (torr)
= 9.80665 × 760000101325× meter of water @ 4°C (mH2O)
= 73.555924006908462867× meter of water @ 4°C (mH2O)
To convert from meter of water @ 4°C (mH2O) to millimeter of mercury (mmHg), use the following formula:
millimeter of mercury (mmHg)
= 9.80665 × 10.133322× meter of water @ 4°C (mH2O)
= 73.556127270818019532× meter of water @ 4°C (mH2O)
To convert from meter of water @ 4°C (mH2O) to pound per square inch (psi), use the following formula:
pound per square inch (psi)
= 9.80665 × 0.00014503768078 × 1000× meter of water @ 4°C (mH2O)
= 1.422333772221187× meter of water @ 4°C (mH2O)
With 0.00014503768078 is the ratio between the base units kilopound per square inch (ksi) and kilopascal (kPa).
To convert from meter of water @ 4°C (mH2O) to kilopound per square inch (ksi), use the following formula:
kilopound per square inch (ksi)
= 9.80665 × 0.00014503768078× meter of water @ 4°C (mH2O)
= 0.001422333772221187× meter of water @ 4°C (mH2O)
With 0.00014503768078 is the ratio between the base units kilopound per square inch (ksi) and kilopascal (kPa).
To convert from meter of water @ 4°C (mH2O) to Inch of mercury (inHg), use the following formula:
Inch of mercury (inHg)
= 9.80665 × 0.00014503768078 × 10.000491154× meter of water @ 4°C (mH2O)
= 2.8959018397919735969× meter of water @ 4°C (mH2O)
With 0.00014503768078 is the ratio between the base units kilopound per square inch (ksi) and kilopascal (kPa).
A meter of water @ 4°C (mH2O) is a metric unit used to measure pressure.
It is precisely defined as 9.80665 kilopascals (kPa).
The specific temperature of 4°C (39.2°F) is key because this is the point where pure water is at its heaviest or most dense (approximately 999.972 kg/m3).
Using this temperature provides a stable and reliable standard for defining pressure.
This precision is essential in scientific and engineering fields like hydraulics and fluid mechanics, ensuring that measurements of pressure head are consistent and accurate across different applications and locations.
The unit "meter of water" (mH2O) is frequently used in civil engineering, hydrology, and irrigation to measure water levels and pressure.
It provides an intuitive way to express the pressure exerted by a column of water, such as the water level in a reservoir, dam, or groundwater well. This measurement is sometimes referred to as the 'piezometric head'.
It is also commonly used to specify the performance of pumps, indicating the height to which a pump can lift water.
For practical use, it's often helpful to know how mH2O converts to other common pressure units.
One mH2O is equal to:
These conversion factors allow engineers and scientists to easily translate pressure specifications between different international and imperial systems.