Free density altitude calculator
Enter your field elevation, altimeter setting, and outside air temperature to see pressure altitude and the density altitude your aircraft and engine truly perform at — updated live, as you type.
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Planning estimate using the FAA/NWS field approximation. Always cross-check your aircraft's published performance data.
Results are estimates. Consult a professional.
How the density altitude calculator works
Density altitude is the altitude your aircraft and engine truly feel, not the number on the field elevation sign. It is pressure altitude corrected for non-standard temperature. The calculator follows the same three steps the FAA teaches: it turns your altimeter setting into a pressure altitude, finds the standard temperature for that height, then adds a correction for how much warmer or cooler the real air is.
What goes into your density altitude
Density altitude is built from three inputs. The calculator shows each step on its own so you can see whether pressure or temperature is driving the result. On most flights, temperature is the larger lever.
Field elevation — the starting point
How high the airport sits above mean sea level. This is fixed for any given field and is where every density altitude calculation begins.
Altimeter setting — the pressure correction
Subtract the altimeter setting from the standard 29.92 inHg and multiply by 1,000. Lower pressure pushes pressure altitude above field elevation; higher pressure pulls it below. One inch of mercury moves it 1,000 feet.
Outside air temperature — the biggest factor
Compare the real temperature with the ISA standard for that pressure altitude. Every degree Celsius above standard adds about 120 feet of density altitude. On a hot day this term dwarfs the pressure correction.
A worked example using the density altitude calculator
A pilot is departing a mountain airport at 5,000 ft elevation. The altimeter setting is 29.45 inHg and the outside air temperature is 25 °C — a warm afternoon. They want the density altitude before checking the takeoff chart.
Step 1 — Find pressure altitude
29.92 − 29.45 = 0.47, and 0.47 × 1,000 = 470 ft. Add field elevation: 5,000 + 470 = 5,470 ft pressure altitude.
Step 2 — Find the ISA standard temperature
At 5,470 ft the standard temperature is 15 − 2 × 5.47 = 4.06 °C. The real air, at 25 °C, is about 21 °C warmer than standard.
Step 3 — Apply the temperature correction
25 − 4.06 = 20.94 °C above standard. Then 5,470 + 120 × 20.94 = 7,983 ft density altitude.
Density altitude by elevation and temperature
This table shows density altitude at a few field elevations and temperatures, all with a standard 29.92 inHg altimeter setting (so pressure altitude equals field elevation). Notice how fast the numbers climb as temperature rises.
| Field elevation | 20 °C | 30 °C | 40 °C |
|---|---|---|---|
| Sea level | 600 ft | 1,800 ft | 3,000 ft |
| 2,000 ft | 3,080 ft | 4,280 ft | 5,480 ft |
| 5,000 ft | 6,800 ft | 8,000 ft | 9,200 ft |
| 8,000 ft | 10,520 ft | 11,720 ft | 12,920 ft |
Density altitude in feet, computed with the FAA field approximation at a standard 29.92 inHg setting. Humidity, not modelled here, raises these figures slightly on muggy days.
How density altitude affects aircraft performance
Thinner air is the whole problem. As density altitude rises the air holds fewer molecules per cubic foot, and three things suffer at once: the wings make less lift, the engine makes less power, and the propeller bites less air. The result is a longer takeoff roll, a weaker climb, and a higher true airspeed needed to fly.
- Longer takeoff roll — the aircraft accelerates more slowly and must reach a higher true airspeed to lift off.
- Reduced climb rate — less excess power means a shallower, slower climb away from terrain and obstacles.
- Reduced engine power — naturally aspirated engines lose power roughly in proportion to the drop in air density.
- Longer landing distance — higher true airspeed at touchdown stretches the rollout, even though indicated airspeed looks normal.
Hot, high, and humid: when density altitude bites
Pilots learn the phrase "hot, high, and humid" because all three push density altitude the same direction — up. A cool morning at a low field is forgiving. A hot afternoon at a mountain strip, with moist air, can erase a large share of your aircraft's performance before you even line up.
Heat is the dominant factor, which is why density altitude peaks in mid-afternoon rather than at noon. Elevation stacks on top of it: a 5,000 ft field on a 30 °C day already feels like 8,000 ft. Humidity adds a smaller correction this calculator does not model — water vapor is lighter than dry air, so very moist conditions raise the true density altitude by a few hundred feet beyond the dry-air figure.
When to use this density altitude calculator
Run it any time the air is non-standard and performance margins are thin — which covers most summer, mountain, and high-load departures.
- Before takeoff at a high or hot field — to read the right line off your aircraft's takeoff and climb charts.
- Mountain flying — where field elevation alone already pushes density altitude into demanding territory.
- Hot summer afternoons — when temperature far above ISA standard quietly steals climb performance.
- Heavy or short-field operations — where a few hundred feet of density altitude can change whether the numbers work.
Density altitude definitions
How accurate is this density altitude calculator?
This is the field approximation taught for the FAA knowledge test, and it is close. The pressure-altitude step is exact, and the 120-feet-per-degree temperature correction tracks the full thermodynamic computation to within a few hundred feet across normal flying conditions. For pre-flight planning and reading performance charts, that is well inside the margins you already build in.
Two caveats. The formula uses dry air, so it slightly understates density altitude on humid days — water vapor is lighter than dry air, adding a few hundred feet in muggy conditions. And it is a planning tool, not a substitute for your aircraft's published performance data: always cross-check takeoff and climb numbers against the charts in your pilot's operating handbook, and treat thin margins conservatively.
Frequently asked questions about the free density altitude calculator
About this Density Altitude calculator
This density altitude calculator runs entirely in your browser. Nothing you enter is sent anywhere — the field elevation, altimeter setting, and temperature you type stay on your device, and the result updates instantly as you adjust them.
It uses the standard FAA/NWS field formula taught for the knowledge test. For more conditions tools, see our other weather calculators, or browse the full library of free calculators.