At what pressure is standard temperature and pressure at sea level defined?

Standard temperature and pressure (STP) at sea level is defined at a pressure of 29.92 inches of mercury (Hg) or 1013.25 hPa (hectopascal). This standardization is crucial for various calculations and measurements in meteorology, aviation, and other fields that require consistent atmospheric data.

At this pressure, the temperature is defined as 15 degrees Celsius (or 59 degrees Fahrenheit). The choice of 29.92 inches Hg stems from historical practices in barometric pressure measurement, where this value has become the accepted standard for sea level reference. Maintaining this convention allows for uniformity in readings and simplifies comparisons across different datasets and operational conditions.

Understanding STP is essential for aircrewman as it affects aircraft performance, navigation, and other operational parameters, particularly in regard to how altitude affects atmospheric conditions.