The ICAO International Standard Atmosphere standard conditions for zero density altitude are 0 meters (0 feet) altitude, 15 deg C (59 deg F) air temp, 1013.25 mb (29.921 in Hg) pressure and 0 % relative humidity ( absolute zero dew point). The standard sea level air density is 1.225 kg/m3 (0.002378 slugs/ft3).