Density Altitude Calculator
Enter the field elevation, altimeter setting, outside air temperature and dew point from the METAR to get pressure altitude, density altitude, the air density ratio and how much engine power and lift you lose. Humidity is included, and a table shows how density altitude changes through the day as it warms up.
Last updated:
Leave empty to calculate for dry air
How to use the Density Altitude Calculator
- Enter the field elevation in feet or meters.
- Enter the altimeter setting (QNH) from the METAR or ATIS in inHg or hPa.
- Enter the temperature and dew point; leave the dew point empty for dry air.
- Read the density altitude, pressure altitude, density ratio and power estimate.
- Check the table to see how much worse it gets as the day warms up, then confirm with your POH charts.
Density altitude formulas used
- Station pressure: P = QNH × ((288.15 − 0.0065 × h) / 288.15)5.25588, with h the field elevation in meters.
- Pressure altitude: PA (ft) = 145,366.45 × (1 − (P / 1013.25 hPa)0.190284). Quick version: PA ≈ elevation + (29.92 − altimeter) × 1,000 ft.
- Vapor pressure from dew point: e = 6.1078 × 107.5·Td / (237.3 + Td) hPa (Magnus/Tetens).
- Virtual temperature: Tv = T / (1 − 0.378 × e / P), in kelvin. Moist air behaves like slightly warmer dry air.
- Density ratio and density altitude: σ = (P / 1013.25) × (288.15 / Tv); DA (ft) = 145,442.16 × (1 − σ0.234969).
- Rule of thumb: DA ≈ PA + 118.8 × (OAT − ISA), where ISA = 15 °C − 1.98 °C per 1,000 ft of pressure altitude. Many pilots round this to 120 ft per °C.
Worked example: a 5,000 ft field, altimeter 29.92 inHg, 30 °C. Pressure altitude is 5,000 ft and ISA there is 5.1 °C, so the air is about 25 °C warmer than standard. The rule of thumb gives 5,000 + 118.8 × 24.9 ≈ 7,960 ft; the exact dry-air result is about 7,800 ft, and a dew point of 10 °C adds roughly 180 ft more. The airplane performs as if it were taking off from a field about 3,000 ft higher than it is.
Standard atmosphere reference
Values from the International Standard Atmosphere (troposphere). If your density altitude matches a row, the air is as thin as the standard air at that altitude.
| Altitude (ft) | ISA temperature | Pressure (inHg) | Density ratio σ | Piston power (Gagg-Ferrar) |
|---|---|---|---|---|
| 0 | 15.0 °C / 59.0 °F | 29.92 | 1.000 | 100% |
| 2,000 | 11.0 °C / 51.9 °F | 27.82 | 0.943 | 93.5% |
| 4,000 | 7.1 °C / 44.7 °F | 25.84 | 0.888 | 87.3% |
| 6,000 | 3.1 °C / 37.6 °F | 23.98 | 0.836 | 81.4% |
| 8,000 | −0.8 °C / 30.5 °F | 22.22 | 0.786 | 75.8% |
| 10,000 | −4.8 °C / 23.4 °F | 20.58 | 0.738 | 70.3% |
| 12,000 | −8.8 °C / 16.2 °F | 19.03 | 0.693 | 65.2% |
Flying with high density altitude
- Take off early. Density altitude is usually lowest just after sunrise and highest in the mid-afternoon. The table above the results shows how much it rises for each step in temperature at your field.
- Use the POH, not a guess. Take the pressure altitude and temperature from this page into your aircraft's takeoff distance and climb rate charts. Add a safety margin for grass, slope, tailwind and pilot technique.
- Reduce weight. Less fuel, fewer passengers or less baggage shortens the takeoff run and improves climb more than anything else you control.
- Lean for best power. In a normally aspirated piston engine, leaning the mixture for the thinner air on the ground before takeoff (per the POH) recovers some of the lost power.
- Remember true airspeed. Your indicated airspeeds for rotation and climb stay the same, but your true airspeed and groundspeed are higher, so the runway goes by faster and landings need more distance.
Frequently asked questions
What is density altitude?
Density altitude is the altitude in the International Standard Atmosphere (ISA) at which the air would have the same density as the air you actually have. Aircraft wings, propellers and normally aspirated engines perform as if they were at the density altitude, not at the field elevation.
How do you calculate density altitude?
First find pressure altitude from the station pressure (or roughly, elevation + 1,000 ft for every inHg the altimeter setting is below 29.92). Then correct for temperature: DA ≈ PA + 118.8 ft × (OAT − ISA temperature). This calculator uses the exact NWS-style method: station pressure and virtual temperature give the density ratio σ, and DA = 145,442 × (1 − σ^0.235) ft.
What is the difference between pressure altitude and density altitude?
Pressure altitude is the altitude in the standard atmosphere with the same pressure; it is what the altimeter reads when set to 29.92 inHg (1013.25 hPa). Density altitude is pressure altitude corrected for non-standard temperature and humidity. On a standard day they are equal; on a hot day density altitude is much higher.
Does humidity really affect density altitude?
Yes, but less than temperature. Water vapor is lighter than dry air, so humid air is less dense. A high dew point on a hot day typically adds a few hundred feet to density altitude. Enter the dew point to include it, or leave it empty for the dry-air value most E6B computers give.
What density altitude is dangerous?
There is no single limit: it depends on the aircraft, weight, runway and obstacles. As a rough guide, a normally aspirated engine loses roughly 3% of its power per 1,000 ft of density altitude, and above about 5,000–8,000 ft many light aircraft need much longer takeoff runs and climb slowly. Always calculate takeoff and climb performance from your POH.
How much engine power is lost at high density altitude?
The calculator uses the Gagg-Ferrar relation for normally aspirated piston engines, P/P₀ = 1.132σ − 0.132, where σ is the density ratio. At a density altitude of 8,000 ft σ is about 0.786, which gives about 76% of sea-level power. Turbocharged engines keep their power to a higher altitude, but wings and propellers still lose efficiency with density.
Which altimeter setting should I use?
Use the current altimeter setting (QNH) from the METAR, ATIS or AWOS for the airport, with the field elevation from the chart supplement. The calculator converts it to station pressure for the field.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.