Standard Atmosphere (atm) is a pressure unit with the symbol atm. One standard atmosphere equals exactly 101,325 pascals. It is used as a reference point, not as a live measurement of local weather pressure.
Quick facts
- Unit name
- Standard Atmosphere
- Symbol
- atm
- Quantity
- pressure
- SI bridge
- 1 atm = 101,325 Pa
- Category
- Pressure
- Converter hub
- Pressure converter
Pressure scale
Pressure units are easiest to compare through pascals. This visual places atm beside neighboring pressure units.
Definition
One standard atmosphere equals exactly 101,325 pascals. It is used as a reference point, not as a live measurement of local weather pressure. Local atmospheric pressure changes with altitude and weather. The unit atm refers to the fixed standard atmosphere, while actual barometric pressure may be higher or lower.
Pressure reference
A pressure number can be gauge, absolute, or differential. The unit atm 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 atm = 101,325 Pa | Useful reference relationship |
| 1 atm = 101.325 kPa | Useful reference relationship |
| 1 atm = 1.01325 bar | Useful reference relationship |
| 1 atm = 760 Torr | Useful reference relationship |
Where atm is used
Atmospheres appear in chemistry, gas laws, diving context, pressure comparisons, vacuum discussions, and educational examples involving atmospheric pressure.
Common mistakes
- Do not assume local air pressure is exactly 1 atm.
- Do not confuse atm as a unit with an automated teller machine in nontechnical writing.
- Do not mix standard atmosphere with technical atmosphere or other historical pressure units.
Converters and formulas
Use these pages when you need a direct calculation involving atm.
Related pressure guides
Compare atm with other pressure units in the same directory.
FAQ
Is 1 atm exactly defined?
Yes. 1 standard atmosphere is exactly 101,325 Pa.
Is atmospheric pressure always 1 atm?
No. Local atmospheric pressure changes with altitude and weather.
Why is atm used in chemistry?
It gives a familiar pressure reference for gas-law examples and laboratory discussions.