Bar is a pressure unit with the symbol bar. One bar equals exactly 100,000 pascals. It is slightly less than one standard atmosphere, which equals 101,325 pascals.
Quick facts
- Unit name
- Bar
- Symbol
- bar
- Quantity
- pressure
- SI bridge
- 1 bar = 100,000 Pa
- Category
- Pressure
- Converter hub
- Pressure converter
Pressure scale
Pressure units are easiest to compare through pascals. This visual places bar beside neighboring pressure units.
Definition
One bar equals exactly 100,000 pascals. It is slightly less than one standard atmosphere, which equals 101,325 pascals. Bar is often written as bar, barg, or bara. The added letters matter: barg means gauge pressure relative to ambient air, while bara means absolute pressure relative to vacuum.
Pressure reference
A pressure number can be gauge, absolute, or differential. The unit bar tells you the scale, but the surrounding notation tells you the reference. Keep labels such as psig, psia, barg, bara, absolute pressure, or differential pressure when the source provides them.
Exact relationships and reference values
| Relationship | Why it matters |
|---|---|
| 1 bar = 100,000 Pa | Useful reference relationship |
| 1 bar = 100 kPa | Useful reference relationship |
| 1 bar = 14.5037738 psi | Useful reference relationship |
| 1 atm = 1.01325 bar | Useful reference relationship |
Where bar is used
Bar is common in compressors, pumps, boilers, pressure washers, espresso machines, dive equipment, industrial gauges, and European vehicle documentation.
Common mistakes
- Do not assume bar and atmosphere are exactly equal; they are close but different.
- Do not drop barg or bara notation when the source provides it.
- Do not use 15 psi per bar for precise specifications.
Converters and formulas
Use these pages when you need a direct calculation involving bar.
Related pressure guides
Compare bar with other pressure units in the same directory.
FAQ
Is bar an SI unit?
No. Bar is accepted in many practical contexts, but the SI pressure unit is the pascal.
Is 1 bar the same as atmospheric pressure?
It is close, but not exact. 1 atm equals 1.01325 bar.
What is barg?
barg means bar gauge, or pressure measured relative to local atmospheric pressure.