Standard Temperature and Pressure
A defined reference condition used to report and compare gas measurements, currently 0 °C and 100 kPa under IUPAC.
Formula / equation
T = 273.15 K, p = 100 kPa
Unit
K, kPa
In depth
Older literature and many textbooks use 1 atm (101.325 kPa) instead of 100 kPa, giving a molar volume of 22.414 L/mol rather than 22.711 L/mol, so the convention in use must always be stated. A separate set of standard ambient conditions (SATP, 25 °C and 100 kPa) is used for thermodynamic data.
Examples in the real world
Quoting a gas yield as 2.24 L at STP means 0.100 mol; comparing engine emissions requires all volumes at a common reference state.