STP or standard temperature and pressure, standard conditions for measurement of the properties of matter. The standard temperature is the freezing point of pure water, 0°C or 273.15°K. The standard pressure is the pressure exerted by a column of mercury (symbol Hg) 760 mm high, often designated 760 mm Hg. This pressure is also called one atmosphere and is equal to 1.01325×10  6 dynes per sq cm, or approximately 14.7 lb per sq in. The density (mass per volume) of a gas is usually reported as its value at STP. Properties that cannot be measured at STP are measured under other conditions usually the values obtained are then mathematically extrapolated to their values at STP.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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