Standard atmosphere (atm)

Quantity: Pressure · Category: Non-SI

The standard atmosphere is a unit of pressure defined as exactly 101,325 pascals — the average air pressure at sea level on Earth. It is the reference pressure for chemistry (STP) and diving.

Relation to SI

1 atm = 101,325 Pa (exact)

Examples

• Atmospheric pressure at sea level is 1 atm by definition.
• A scuba diver 10 m down experiences about 2 atm absolute.
• Standard temperature and pressure (STP) uses 1 atm as the reference.