standard temperature and pressure are defined as _____.
Definition. Standard Temperature and Pressure (STP) is defined as 0 degrees Celsius and 1 atmosphere of pressure. Do not confuse STP with the STP Products Company, a maker of oil and fuel additives...unless you are reading one of their MSDS's! Additional Info. STP is used in many thermodynamic calculations and tabulations. Certain properties of matter such as density, viscosity, boiling point etc. will vary with changes in temperature or pressure. Having one common set of conditions (state) for tabulating these values makes comparisons possible and eases calculations.