What is density altitude?

Density altitude is pressure altitude corrected for non-standard temperature and humidity. It is the altitude in the standard atmosphere at which the air has the density you are actually experiencing. High density altitude means thin air and reduced performance.

What formula is used?

The tool uses the standard approximation: density altitude equals pressure altitude plus 118.8 feet for every degree Celsius the temperature is above the ISA temperature at that altitude. ISA at sea level is 15 degrees, lapsing 1.98 degrees per 1000 feet.

Why does humidity raise density altitude?

Water vapour is lighter than dry air, so humid air is less dense than dry air at the same temperature and pressure. Higher dew points mean more vapour, which lowers density and therefore raises density altitude, hurting performance further.

Why does high density altitude reduce performance?

Engines make less power, propellers and wings produce less thrust and lift, and true airspeed for a given indicated airspeed rises, all because the air is thinner. Takeoff roll lengthens and climb rate falls, which matters most on hot, high, humid days.

Is the humidity correction precise?

It is a small approximate term based on the dew point spread and is optional. For most light-aircraft planning the dry-air density altitude dominates, but on very humid days the extra few hundred feet can be the difference in a marginal takeoff.

Density Altitude Calculator

On a hot, high, humid day an aircraft can perform as though it is thousands of feet higher than the runway elevation suggests. Density altitude captures that effect in a single number, and this calculator derives it from pressure altitude, temperature, and an optional dew point.

How it works

The core relationship scales the temperature deviation from the standard atmosphere at your pressure altitude, with an optional humidity term:

ISA temp (°C) = 15 − 1.98 × (pressure altitude / 1000)
ΔT = OAT − ISA temp
density altitude ≈ pressure altitude + 118.8 × ΔT  (+ humidity term)

The 118.8 feet per degree Celsius is the standard sensitivity of density altitude to temperature. When a dew point is supplied, a small correction is added because moist air is less dense than dry air, which raises the effective altitude.

Example and notes

At a pressure altitude of 5,000 feet with an outside air temperature of 30 °C, the ISA temperature is 15 − 1.98 × 5 = 5.1 °C, so ΔT is about 24.9 °C and the dry density altitude is roughly 5,000 + 118.8 × 24.9 ≈ 7,960 feet. A high dew point on top of that can push it past 8,000 feet equivalent. Always cross-check performance against the aircraft’s charts using density altitude, never the bare field elevation, on hot or high days.