Military utility tools / Density altitude
Density altitude
Field elevation, QNH, temperature and dew point in. Pressure and density altitude in metres out.
Set the inputs, then work it out.
Pressure altitude--m
Density altitude--m
ISA deviation--°C
ISA temperature--°C at this level
Air density--kg/m³
Relative density--%of sea level
Station pressure--hPa
Relative humidity--%from dew point
Why is density altitude higher than the field elevation?
Because standard atmosphere assumes a specific temperature for each height, and warm air is thinner than that standard. Every degree above ISA pushes density altitude up by roughly thirty-six metres, which is why a hot afternoon at a high field is a very different proposition from a cold morning at the same place.
Does humidity really matter?
Less than temperature, but it runs the same way. Water vapour is lighter than the nitrogen and oxygen it displaces, so humid air is less dense. On a hot humid day the contribution is worth tens of metres of density altitude.