Answer: STP in chemistry is the abbreviation for Standard Temperature and Pressure. STP most commonly is used when performing calculations on gases, such as gas density. The standard temperature is 273 K (0° Celsius) and the standard pressure is 1 atm pressure. At STP, one mole of gas occupies 22.4 L of volume (molar volume). STP commonly is used when standard state conditions are applied to calculations. Standard state conditions, which include standard temperature and pressure, may be recognized in calculations by the superscript circle.