standard temperature and pressure. Abbreviated as STP is a commonly used term in calculations involving gas, is now we're going to say at STP the temperature is measured as either zero degrees Celsius or 273. Kelvin. Now we know that when we're dealing with gas calculations, we tend to go with Kelvin. Now the pressure at STP is one atmosphere. So just remember, when you hear STP, it means 273.15 Kelvin and for pressure, one atmosphere.