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.