21st October 2019


What is standard ambient temperature and pressure?

An unofficial, but commonly used standard is standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.987 atm).

What is meant by ambient pressure?

The ambient atmospheric pressure at sea level is not constant: it varies with the weather, but averages around 100 kPa. One bar is 100 kPa or approximately ambient pressure at sea level. Ambient pressure may in other circumstances be measured in pounds per square inch (psi) or in standard atmospheres (atm).

Is NTP and STP same?

STP is set by the IUPAC as 0°C and 100 kPa or 1 bar. Many old books and online sources say that standard pressure is 101.325 kPa (the old IUPAC standard that was changed in 1982), but I defer to the current IUPAC standard of 100 kPa. NTP is set at 101.325 kPa but uses 20°C as the temperature.
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