# What is the density altitude?

Density altitude calculator for pilots: density altitude from field elevation, altimeter setting, temperature and dew point, with the pressure altitude, the ISA temperature and the 118.8 ft per °C rule of thumb.

- Page: https://www.acalculator.org/physics/density-altitude-calculator
- JSON spec: https://www.acalculator.org/physics/density-altitude-calculator.json
- Version: 810d5503b6aa

## Default answer

Example with the default inputs (Field elevation 5,000 ft, Altimeter setting 29.92 inHg, Outside air temperature 85.9999999999999 °F): The density altitude is 7,821 ft (pressure altitude 5,001 ft).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| elev | Field elevation | The elevation of the airport or place, above mean sea level. |
| alt | Altimeter setting | The altimeter setting (QNH) from ATIS, METAR or the tower. |
| t | Outside air temperature | The air temperature at the field. |
| td | Dew point | The dew point at the field, for the humidity. Leave empty for dry air. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| da | Density altitude | The height in the standard atmosphere with the same air density. |
| pa | Pressure altitude | Field elevation + the altimeter correction (NWS formula). |
| rule | Rule of thumb | Pressure altitude + 118.8 ft × (temperature − ISA temperature in °C), for dry air. |
| isa | ISA temperature (°C) | The standard-atmosphere temperature at the pressure altitude: 15 − 1.9812 per 1,000 ft. |
| stationHpa | Station pressure (hPa) | The actual pressure at the field in hectopascals. |
| stationInHg | Station pressure (inHg) | The actual pressure at the field in inches of mercury. |
| vapourHpa | Vapour pressure (hPa) | The water vapour pressure from the dew point (0 for dry air). |
| virtualC | Virtual temperature (°C) | The temperature dry air would need to have the same density as this moist air. |
| ratio | Density ratio (%) | 17.326 × P ÷ Tv: the air density as a percentage of standard sea-level density. |

## Method

PA = elevation + 145,366.45 × (1 − (A ÷ 1,013.25)^0.190284) ft; P = 1,013.25 × (1 − PA ÷ 145,366.45)^(1 ÷ 0.190284) hPa; e = 6.11 × 10^(7.5Td ÷ (237.7 + Td)) hPa; Tv = T ÷ (1 − (e ÷ P) × 0.378) K; DA = 145,442.16 × (1 − (17.326 × P_inHg ÷ (1.8 × Tv))^0.235) ft.

## Assumptions

- The standard atmosphere: 1,013.25 hPa and 15 °C at sea level, cooling 1.9812 °C per 1,000 ft.
- Leave the dew point empty for dry air; humidity raises density altitude, often by a few hundred feet on a warm, humid day.

## Worked examples

1. elev = 0, alt = 101,325, t = 288.15 gives pa = 0, isa = 15, da = 5.109212. Source: Wikipedia, Density altitude (DA = 145,442.16 × (1 − [17.326 × P ÷ T]^0.235), P in inHg, T in °R; DA ≈ PA + 118.8 × (OAT − ISA)), https://en.wikipedia.org/wiki/Density_altitude (retrieved 2026-10-05); Wikipedia, Pressure altitude (145,366.45 × [1 − (p ÷ 1,013.25)^0.190284] ft), https://en.wikipedia.org/wiki/Pressure_altitude (retrieved 2026-10-05).
2. elev = 1,524, alt = 101,320.748119, t = 303.15 gives da = 2,383.991103, rule = 2,426.289306, stationHpa = 842.970887. Source: Wikipedia, Density altitude (DA = 145,442.16 × (1 − [17.326 × P ÷ T]^0.235), P in inHg, T in °R; DA ≈ PA + 118.8 × (OAT − ISA)), https://en.wikipedia.org/wiki/Density_altitude (retrieved 2026-10-05).
3. elev = 1,524, alt = 101,320.748119, t = 303.15, td = 293.15 gives vapourHpa = 23.340674, da = 2,487.578042. Source: MetPod, Density Altitude (DA) Calculation, NOAA formulas e = 6.11 × 10^(7.5Td ÷ (237.7 + Td)) and Tv = T ÷ (1 − (e ÷ p)(1 − 0.622)), https://www.metpod.co.uk/calculators/density-alt/ (retrieved 2026-10-05); Wikipedia, Density altitude (DA = 145,442.16 × (1 − [17.326 × P ÷ T]^0.235), P in inHg, T in °R; DA ≈ PA + 118.8 × (OAT − ISA)), https://en.wikipedia.org/wiki/Density_altitude (retrieved 2026-10-05).

## FAQ

### How do you calculate density altitude?

Find the pressure altitude and the station pressure, then the density altitude from the air density: DA = 145,442.16 × (1 − (17.326 × P ÷ T)^0.235) ft, with P the station pressure in inHg and T the (virtual) temperature in °R. A 5,000 ft field at 29.92 inHg and 30 °C in dry air gives about 7,821 ft.

### What is the rule of thumb for density altitude?

DA ≈ pressure altitude + 118.8 ft for each °C the air is warmer than the standard temperature. Many pilot guides round this to 120 ft per °C. It ignores humidity.

### Why does density altitude matter?

Engines make less power, propellers and wings get less lift, and the aircraft needs a longer takeoff roll and climbs more slowly when the air is thin. Performance charts use density altitude for this.

### Does humidity raise density altitude?

Yes. Water vapour is lighter than dry air, so humid air is less dense. On a 30 °C day at a 5,000 ft field, a 20 °C dew point raises the density altitude by about 340 ft.

### What is the standard temperature at altitude?

The standard atmosphere is 15 °C at sea level and cools about 1.98 °C per 1,000 ft (6.5 °C per km), so it is about 5 °C at 5,000 ft.

### Is density altitude the same as pressure altitude?

Only on a standard day. Pressure altitude corrects for pressure alone; density altitude also corrects for temperature and humidity.

## Sources

- Wikipedia, Density altitude: DA = 145,442.16 × (1 − [17.326 × P ÷ T]^0.235) and DA ≈ PA + 118.8 × (OAT − ISA), retrieved 2026-10-05. https://en.wikipedia.org/wiki/Density_altitude
- Wikipedia, Pressure altitude: h = 145,366.45 × [1 − (p ÷ 1,013.25)^0.190284] ft, retrieved 2026-10-05. https://en.wikipedia.org/wiki/Pressure_altitude
- MetPod, Density Altitude (DA) Calculation: the NOAA vapour pressure and virtual temperature formulas, retrieved 2026-10-05. https://www.metpod.co.uk/calculators/density-alt/
- National Weather Service, Density Altitude Calculator, retrieved 2026-10-05. https://www.weather.gov/epz/wxcalc_densityaltitude