STP is the abbreviation for Standard Temperature and Pressure. The IUPAC definition is that STP is 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 105 Pa (100 kPa, 1 bar). Different organizations use other values. For example, NIST defines STP as a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). If you perform calculations, it’s useful to know that one mole of gas occupies 22.4 L of volume (molar volume) at STP.
When Is STP Used?
You’ll encounter STP in chemistry and physics, when performing calculations involving gases, such as density.
STP is used when standard state conditions apply to calculations. You can recognize standard state conditions because they are denoted using the superscript circle. For example, ΔS° is the change in entropy at STP.