Standard Temperature and Pressure (STP) is the international standard combination of temperature and pressure used when measuring the density and other characteristics (e.g. solid, liquid or gaseous) for elements, chemicals, substances and other materials.

Because materials change state under different pressure and temperature conditions, an international standard coupling an easily measured absolute pressure and temperature was established known as STP, which is the abbreviation for Standard Temperature and Pressure.  

Since 1982, STP is defined as:

1. 273.15 K (Degrees Kelvin)
2. 100000 Pa (Pascals of pressure)

STP (pressure)

The STP (pressure) is 10⁵ pascals (Pa) or 1 bar.  The equivalent values of standard pressure include:

• 100,000 pascal
• 100 kPa
• 750.06375542 mmHg  (millimeters of mercury)
• 29.5299888 inHg  (inches of mercury)
• 0.98692327 atmospheres
• 10 Netwons per square centimeter
• 14.50377377 psi (pounds per square inch)
• 750.06150504 Torr

STP (temperature)

The STP (temperature) is 273.15 degrees Kelvin (0 °C, 32°F).  The equivalent values of Standard Temperature are also:

• 0 °C
• 32 °F
• 491.67 °R (rankine)