What Is Bar (bar)?
A bar is a unit used to measure pressure. Pressure tells us how much force is pressing on an area, like air pushing on your skin or water pressing on a diver.
One bar is almost the same as the air pressure at sea level on Earth. It is equal to 100000 pascals, which is the main pressure unit in the SI system.
Definition
In science, the bar is defined in a clear and exact way:
- 1 bar is exactly 100000 pascals (Pa).
The pascal is the SI unit of pressure. It means one newton of force spread over one square meter. So the bar is just a bigger and easier number that many people like to use instead of very large pascal numbers.
Because 1 bar is close to normal air pressure, it is very handy in weather reports, scuba diving, and many engineering jobs.
History / Origin
The bar was created in the early 1900s by scientists who studied the weather and the atmosphere. They wanted a simple unit for air pressure that felt close to everyday values.
They chose the value of 100000 pascals because it is:
- a round and easy number
- very close to the average air pressure at sea level on Earth
For many years, weather maps and forecasts used the millibar, which is one thousandth of a bar. Later, the pascal became the official SI unit of pressure. Today, scientists are encouraged to use pascals, but the bar is still common in many real world fields.
Symbol & Abbreviation
Here are the main symbols used with the bar:
- bar is the unit name.
- bar is also the official symbol. It does not use capital letters.
Common multiples and submultiples are:
- millibar (often written mbar or mb) which is 0.001 bar.
- bar for the base unit.
In modern weather reports, the millibar is often replaced by the hectopascal (hPa). Numbers in hPa and mbar are the same size. For example, 1013 hPa is the same pressure as 1013 mbar.
Current Use Around the World
Even though the pascal is the main SI unit, the bar is still widely used in many areas:
- Meteorology Weather experts still use millibars or hectopascals which match old millibar values to show air pressure on weather maps.
- Scuba diving Dive computers and tanks often show pressure in bar so divers can easily see how much air they have and how deep they are.
- Ocean science Some ocean studies use the bar to show water pressure at different depths.
- Engineering and industry Many systems, such as pumps, compressors, and refrigeration units, use bar to show working pressure.
- Everyday tools In some countries, tire gauges, pressure washers, and other tools show pressure in bar instead of psi.
Even though the bar is not an official SI unit, it is still accepted in many technical fields because it is very practical and easy to understand.
Example Conversions
Here are some simple conversions between bar and other common pressure units.
Between bar and pascal (Pa)
- 1 bar = 100000 Pa
- 0.5 bar = 50000 Pa
- 2 bar = 200000 Pa
To change bar into pascals, multiply by 100000. To change pascals into bar, divide by 100000.
Between bar and kilopascal (kPa)
- 1 bar = 100 kPa
- 1 kPa = 0.01 bar
- 2.5 bar = 250 kPa
This is very simple because 1 bar is exactly 100 kilopascals.
Between bar and standard atmosphere (atm)
- 1 bar is about 0.99 atm
- 1 atm is about 1.01 bar
So you can think of 1 bar as almost the same as 1 atmosphere of pressure at sea level.
Between bar and pounds per square inch (psi)
- 1 bar is about 14.5 psi
- 1 psi is about 0.07 bar
- 2 bar is about 29 psi
This is useful for comparing car tire pressures. For example, 2.5 bar is about 36 psi.
Between bar and millimeter of mercury (mmHg)
- 1 bar is about 750 mmHg
- 760 mmHg is about 1.01 bar
Millimeters of mercury are often used in medicine to measure blood pressure.
Related Units
Many other units are used to measure pressure. Here are some that are closely related to the bar:
- Pascal (Pa) The SI base unit of pressure. 1 bar = 100000 Pa.
- Kilopascal (kPa) One thousand pascals. 1 bar = 100 kPa.
- Hectopascal (hPa) Often used in weather reports. 1 hPa has the same value as 1 millibar.
- Millibar (mbar or mb) 0.001 bar. Very common in older meteorology texts.
- Standard atmosphere (atm) A unit based on average sea level pressure. 1 atm is about 1.01325 bar.
- Millimeter of mercury (mmHg) A pressure unit based on a column of mercury. Common in medicine.
- Pounds per square inch (psi) A pressure unit used in the United States, often for car tires and tools.
FAQs
Is bar an SI unit?
No. The bar is not an official SI unit. The SI pressure unit is the pascal (Pa). However, the bar is still accepted and widely used because it is simple and practical.
How big is 1 bar compared to air pressure at sea level?
Normal air pressure at sea level is about 1.01325 bar. So 1 bar is very close to everyday air pressure on Earth. You can think of 1 bar as almost exactly sea level air pressure.
When is bar used instead of pascal?
People use bar when pascal numbers would be too big or awkward. In diving, weather reports, and many machines, pressures are usually between about 0.1 bar and a few bar. These are easy numbers to read and remember.
What is the difference between bar and millibar?
A millibar is much smaller than a bar. One bar equals 1000 millibar. So:
- 1 bar = 1000 mbar
- 1 mbar = 0.001 bar
Weather maps often show air pressure in millibar or in hectopascal which has the same number values.
How can I quickly change bar into psi or atm in my head?
Here are two simple tricks:
- Bar to atm 1 bar is almost 1 atm. For most simple problems, you can treat them as equal.
- Bar to psi 1 bar is about 15 psi. So multiply bar by 15 to get a quick estimate in psi. For example, 2 bar is about 30 psi.
These shortcuts are not perfect, but they are good enough for everyday use and quick checks.
