Thread:Therefir/@comment-24503208-20180418194659

Source is here: https://www.skybrary.aero/index.php/International_Standard_Atmosphere_(ISA)

This is also reinforced by another source: https://wahiduddin.net/calc/density_altitude.htm

"As an example, using the ISA standard sea level conditions of P = 101325 Pa and T = 15 deg C, the air density at sea level, may be calculated as:

D = (101325) / (287.05 * (15 + 273.15)) = 1.2250 kg/m3" 