Atmosphere (atm)

Quantity: pressure · Category: Pressure

The standard atmosphere is a unit of pressure originally defined as the average atmospheric pressure at sea level. It remains the reference pressure for standard-state definitions in thermochemistry and for the '1 atm' standard used throughout gas-law problems. It is exactly 101325 pascals by definition.

Relation to SI

1 atm = 101325 Pa exactly

Examples

• The older STP definition was 1 atm and 0 °C
• Standard-state Gibbs energies are tabulated at 1 atm for gases
• Car tire pressures of ~2–3 atm are commonly quoted in atm