Convert Pressure from meters of water @ 4°C to bar (mH₂O to bar)

Meter of Water Column to Bar Conversion Formula

To convert pressure from meters of water column (mH2O) to bar, multiply by 0.0980665.

• bar = mH2O × 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:

• 1 bar ≈ 10.197 mH2O — close enough to "10 meters of water per bar" for quick mental checks, with a 2% error you then refine.

Step-by-Step Example

A borehole pump must lift water 85 m to the surface tank (its static head). The pressure this represents at the pump outlet:

1. Take the head: 85 mH2O
2. Multiply by 0.0980665: 85 × 0.0980665 = 8.336 bar

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.

Quick Reference Table

Head vs Pressure — Why Pump Engineers Need This Constantly

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.

How many meters of water @ 4°c are in one bar? One bar (bar) contains 10.197162129779282426 meters of water @ 4°C (mH₂O) — the inverse of the factor above. Multiplying by 0.0980665 takes you from meters of water @ 4°c to bar; multiplying by 10.197162129779282426 brings you back.

Put in words: one meter of water @ 4°c equals 0.0980665 bar, so the meter of water @ 4°c is the smaller unit of this pair. Converting between them never changes the amount of pressure being measured — only the size of the unit you count it in.

What is a meter of water @ 4°C (mH₂O)?

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 Significance of 4°C in Water Pressure

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.

Practical Uses in Engineering and Hydrology

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.

Conversion to Other Common Pressure Units

For practical use, it's often helpful to know how mH₂O converts to other common pressure units.

One mH₂O is equal to:

• 9.80665 kilopascals (kPa)
• 9806.65 Pascals (Pa)
• 0.098 bar (approximately)
• 1.422 pounds per square inch (psi) (approximately)

These conversion factors allow engineers and scientists to easily translate pressure specifications between different international and imperial systems.

What is a bar (bar)?

The bar is a metric unit of pressure.

It is defined as exactly 100 kilopascals (kPa), or 100,000 Pascals (Pa).

Although it is not an official part of the International System of Units (SI), it is widely accepted for use with the SI. The bar is a popular unit for measuring pressure because it is very close to the average atmospheric pressure on Earth at sea level.

Origin of the Bar

The term "bar" comes from the Greek word βάρος (baros), which means "weight."

The unit was introduced by British meteorologist William Napier Shaw in 1909. It is still widely used in meteorology, oceanography, and engineering.

Bar vs. Standard Atmosphere (atm)

A common point of confusion is the difference between a bar and a standard atmosphere (atm).

While they are very close in value, they are not the same:

• 1 bar = 100,000 Pascals (Pa)
• 1 atmosphere (atm) = 101,325 Pascals (Pa)

This means 1 bar is approximately equal to 0.987 atm. Because it's so close to atmospheric pressure and is a round number (100 kPa), the bar is a very convenient unit for many applications.

Common Applications of the Bar

The bar is a versatile unit used to measure pressure in many industrial and everyday contexts.

Common examples include:

• Automotive: Measuring tire pressure (often listed on a car's door jamb alongside PSI).
• Scuba Diving: Expressing the amount of air pressure inside diving tanks.
• Weather: Used by meteorologists for weather forecasting and reading atmospheric pressure.
• Plumbing & Pumps: Measuring water pressure in pipes and pump systems.
• Industrial: Measuring air pressure in pneumatic equipment and gas pressure in cylinders for welding.

meter of water @ 4°C to bar Conversion Table

Here are some quick reference conversions from meter of water @ 4°C (mH₂O) to bar (bar):

This conversion in other languages

Engineering datasheets across Europe write meter of water @ 4°C to bar several different ways. The calculation is the same in every one of them.