What is bar?
A bar is a pressure unit approximately equal to standard atmospheric pressure, or 100,000 pascals. It is widely used in meteorology, hydraulics, diving equipment, and industrial pressure gauges.
Real-world uses
Bars are widely used in European tyre pressure specifications, compressed gas cylinder ratings, scuba diving depth gauges, and industrial process controls. Espresso machines operate at 9–15 bar. Atmospheric pressure is approximately 1.013 bar.
History
The bar was introduced by Norwegian meteorologist Vilhelm Bjerknes in 1909, derived from the Greek word "baros" meaning weight. Though not an SI unit, it is widely accepted in industry and was retained in the EU Directive on units of measurement.
Common mistakes
Confusing bar with atm—they are close (1 atm ≈ 1.01325 bar) but not identical. Also, gauge pressure (barg) versus absolute pressure (bara) is often mixed up; gauge pressure reads zero at atmospheric pressure.
What is atmosphere?
An atmosphere (atm) is a pressure unit equal to mean atmospheric pressure at sea level, approximately 101,325 pascals. It is used as a reference in chemistry, diving tables, and altitude calculations.
Real-world uses
Atmospheres are used as a reference pressure in chemistry (standard conditions: 1 atm, 25°C), scuba diving (each 10 m of seawater adds about 1 atm), and high-pressure industrial applications like autoclaves and pressure vessels.
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0°C under standard gravity. Evangelista Torricelli first measured atmospheric pressure in 1644 using a mercury barometer, establishing this foundational concept.
Common mistakes
Confusing standard atmosphere (101,325 Pa) with technical atmosphere (1 kgf/cm² ≈ 98,066.5 Pa). Also, assuming atmospheric pressure is constant at 1 atm everywhere—it varies with altitude, weather, and temperature.
When is this conversion used?
Tyre pressure gauges, HVAC systems, and industrial equipment may use different pressure units depending on the manufacturer and region. Converting between psi, bar, and kPa is common in automotive and engineering work.
Worked examples
1 bar = 0.98692327 atmosphere
1 atmosphere = 101,325 pascal
How to convert bar to atmosphere
To convert bar to atmosphere, multiply the value by 0.98692327.
To convert atmosphere back to bar, multiply by 1.01325.
Measurement standards
The pascal (Pa) is the SI derived unit of pressure, defined as one newton per square metre. The World Meteorological Organization mandates the hectopascal (hPa) for atmospheric pressure reporting in aviation and weather services.
Did you know?
The pressure at the bottom of the Mariana Trench, nearly 11 km deep, exceeds 1,086 bar — over a thousand times atmospheric pressure. At this depth, water is compressed by about 5%, making it measurably denser than at the surface.
Quick reference: bar to atmosphere
| bar | atmosphere |
|---|---|
| 0.1 | 0.09869233 |
| 0.5 | 0.49346163 |
| 1 | 0.98692327 |
| 2 | 1.97384653 |
| 5 | 4.93461633 |
| 10 | 9.86923267 |
| 25 | 24.67308167 |
| 50 | 49.34616334 |
| 100 | 98.69232667 |
| 250 | 246.73081668 |
| 500 | 493.46163336 |
| 1,000 | 986.92326672 |
Common values
| bar | atmosphere | |
|---|---|---|
| Car tyre | 2.2 bar | 2.17123119 atmosphere |
| Standard atmosphere | 1.01325 bar | 1 atmosphere |
| Blood pressure (systolic) | 0.16 bar | 0.15790772 atmosphere |
| Deep-sea submersible | 1,100 bar | 1,085.61559339 atmosphere |
| Bicycle tyre | 6.2 bar | 6.11892425 atmosphere |