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Density altitude: what it is and how to calculate it before a VFR flight

Density altitude explains why, on hot days or with low pressure, an aircraft may perform as if it were at a higher elevation.

By FlightDesk

Density altitude is the altitude at which an aircraft effectively performs according to air density. It does not necessarily match the aerodrome elevation: high temperature and low pressure reduce air density and increase density altitude.

Why it matters before take-off

With less dense air, engine, propeller and wing work in less favourable conditions. Take-off roll may increase and initial climb performance may reduce. Use this figure to understand the conditions, then consult the approved AFM/POH performance data for the aircraft.

A practical sequence

Read METAR and TAF, check QNH and temperature, calculate pressure altitude and density altitude, then compare the result with the applicable aircraft performance charts. Density altitude is a planning aid, not a take-off clearance.

References

Further reading

EASA Easy Access Rules for Air Operations FlightDesk – Pressure and wind calculator
Frequently asked questions

Common questions

What is the difference between pressure altitude and density altitude?

Pressure altitude is based on pressure; density altitude further reflects temperature and air density.

Does density altitude increase in hot weather?

Normally yes: at the same pressure, warmer air is less dense and density altitude increases.

Keep reading
Operations QNH, Altitude and Flight Level Use QNH and standard pressure correctly, distinguish transition altitude from transition level and cross-check the altimeter before departure. Weather VFR Weather METARs and TAFs describe airport conditions and time windows; radar, wind, precipitation and clouds complete the picture along the route. Flight planning VFR Flight Planning Turn a route into a structured sequence covering the aircraft, reporting points, distances, times, altitudes, radio frequencies and fuel.