What is the specific gravity of air?

The specific gravity of air is defined as the ratio of the density of air to the density of a reference substance, typically dry air at standard conditions being compared to the density of water. At standard temperature and pressure (STP), the density of air is approximately 1.225 kg/m³, while the density of water is about 1000 kg/m³. This relationship results in a specific gravity for air that is close to 1.000 when considering air at sea level under standard conditions.

Using 1.000 as the specific gravity of air allows for easy comparison with other gases or substances, since it signifies that air is slightly lighter than water, facilitating various calculations in aerodynamics and flight mechanics. Understanding the specific gravity of air is fundamental in fields such as meteorology and aviation, where density differences influence buoyancy, lift, and overall aircraft performance.

This is why the stated answer accurately reflects the standard conventions in science and aviation.