Standard temperature and pressure (STP) or Standard conditions for temperature and pressure are various standard sets of conditions for experimental measurements used to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted.

Other organizations have established a variety of other definitions. In industry and commerce, the standard conditions for temperature and pressure are often necessary for expressing the volumes of gases and liquids and related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure): standard cubic meters per second (Sm3/s), and normal cubic meters per second (Nm3/s).

STP conditions are important to calculate and express fluid flow rates and the volumes of liquids and gases when standard state conditions are applied. These properties are also highly dependent on temperature and pressure conditions and changes. Adopting and stating standard conditions enable similar experiments to occur in similar laboratory conditions and to generate similar and comparable results. It also makes it easier to compare different measurements for gases, such as the moles (mol) of gas in a given volume. Both temperature and air pressure vary from one place to another.