Under standard conditions, what pressure measurement relates to standard atmospheric pressure?

The measurement that corresponds to standard atmospheric pressure under standard conditions is 29.92 inches of mercury. This value is based on the barometric pressure at sea level and is a commonly used reference point in aviation and meteorology for various calculations.

Standard atmospheric pressure is defined as the pressure exerted by a mercury column that is 29.92 inches high at sea level at a temperature of 0 degrees Celsius. This standard is important for various applications, including altimetry, where pressure measurements are used to determine altitude.

The other measurements provided do not correspond to standard atmospheric pressure. For instance, 20.9 inches of mercury is less than the standard pressure and may reflect conditions at higher elevations or other environmental variations. Likewise, the psi values (15 psi and 14.0 psi) relate to pressure in different contexts—14.0 psi is often associated with gauge measurements at sea level and is approximately equivalent to 29.92 inches of mercury, but it does not directly represent the standard atmospheric pressure as a measurement of altitude or barometric conditions.

Thus, 29.92 inches of mercury is the accurate representation of standard atmospheric pressure, reflecting its significance in aviation and related fields.