What is the volume of air at 15psi?

Answer 1

The qustion should be rephrased to "What is the DENSITY of air at 15 psi." Volume is independent of mass, i.e. one cubic foot is one cubic foot regardless of pressure. Density refers to how much mass there is per unit volume. At 15 psi or, more accurately 14.7 psi, (atmospheric pressure at sea level) the density of air is 0.0805 pounds per cubic foot (pcf). Not much. This is commonly called one "atmosphere." Compare that with 62.4 pcf for fresh water and about 64 pcf for sea water. I ran some quick numbers and found that for each 33 feet of sea water depth the pressure increases by one atmosphere (14.7 psi.) The common recreational dive depth limit of 60 feet corresponds to just under 3 atmospheres, including 27 psi water pressure plus 14.7 air pressure above the water for a total of about 42 psi.