Density Altitude Calculator

Introduction: Why density altitude matters for aircraft performance

Density altitude (DA) is a way to express air density as an “equivalent altitude” for flight planning. When air becomes less dense—because the field is high, the temperature is above standard, or the pressure is lower—an airplane performs as if it were operating from a higher runway elevation than the number painted on the ramp. In practice, rising density altitude usually shows up as:

• Longer takeoff rolls and slower acceleration
• Reduced climb rate and weaker obstacle clearance
• Less efficient propeller or rotor performance
• Lower engine output for normally aspirated engines

This calculator gives a planning estimate, not a substitute for aircraft-specific performance charts. For operational decisions, cross-check the result against the POH/AFM, runway length, wind, slope, contamination, and the current weather report.

What to enter for a density altitude check

• Field elevation (MSL): Enter the airport elevation above mean sea level, not height above ground. The airport diagram, chart supplement, or airport information block usually lists it.
• Outside air temperature (OAT): Use the temperature at the field, typically from a METAR or ATIS report. Make sure the number matches the unit you choose in the form.
• Altimeter setting: Use the current altimeter setting from METAR/ATIS, such as 29.92 inHg or 1013 hPa. This is the setting used for pressure altitude, not station pressure.

How this density altitude calculator estimates the result

This density altitude calculator follows the common preflight workflow: first it turns the airport elevation and altimeter setting into pressure altitude, then it compares the outside air temperature with the ISA temperature at that altitude and applies a temperature correction.

Step 1: Pressure altitude (PA)

Pressure altitude is the altitude indicated when the altimeter is set to standard pressure (29.92 inHg / 1013.25 hPa). A widely used approximation is:

where PA and Elev are in feet and Alt is the altimeter setting in inHg. If you enter meters or hPa, the calculator converts those inputs into working units first, then converts the final answer back to feet and meters for display.

Step 2: ISA temperature at that altitude

ISA uses a sea-level temperature of 15 °C and a near-sea-level lapse rate of about 2 °C per 1,000 ft. A simple standard-temperature estimate at the pressure altitude is:

ISA Temp (°C) ≈ 15 − 2 × (PA/1000)

Step 3: Density altitude (DA) via temperature correction

The common rule-of-thumb correction is about 120 ft for each °C of temperature difference from ISA:

DA ≈ PA + 120 × (OAT − ISA Temp)

Interpreting your density altitude result

• DA close to field elevation: The air mass is near standard for that airport, so performance should stay closer to the POH/AFM numbers for the actual elevation.
• DA much higher than field elevation: Expect noticeably worse takeoff and climb performance. Check runway length, obstacle clearance, aircraft weight, and any density-altitude limit in your operating procedures.
• Negative DA: Very cold, high-pressure days can produce a negative density altitude. That often helps performance, but you should still verify with the aircraft charts and the rest of the operating environment.

Worked example: hot-day density altitude at a 5,000 ft field

Given:

• Field elevation: 5,000 ft MSL
• Altimeter setting: 29.62 inHg
• OAT: 30 °C

1) Pressure altitude:

PA = 5,000 + (29.92 − 29.62) × 1000 = 5,000 + 0.30 × 1000 = 5,300 ft

2) ISA temperature at PA:

ISA Temp ≈ 15 − 2 × (5.3) = 15 − 10.6 = 4.4 °C

3) Density altitude:

DA ≈ 5,300 + 120 × (30 − 4.4) = 5,300 + 120 × 25.6 = 5,300 + 3,072 = 8,372 ft (≈ 2,552 m)

On that day, the airplane behaves as though it is departing from a much higher airport, which is why the takeoff run and climb performance feel noticeably worse even though the runway elevation is only 5,000 ft.

Quick comparison: how weather changes density altitude

Limitations, assumptions, and safety notes

• Approximation method: The calculator uses common training rules of thumb—an ISA lapse approximation and about 120 ft per °C. Real atmosphere behavior and aircraft performance charts may differ.
• Humidity not included: High humidity reduces air density and can raise density altitude a little. Because humidity is not an input here, the estimate can run slightly low on hot, muggy days.
• Altimeter setting vs station pressure: METAR altimeter setting is not the same thing as station pressure. Using the wrong pressure value can shift the answer.
• Valid ranges: Very high elevations and extreme temperatures can make a simple lapse-rate model less accurate.
• Rounding & conversions: Unit conversions and rounding may produce small differences from avionics or EFB tools that use more detailed models.
• Not operational authorization: This page is for estimation and education. Always confirm takeoff and climb performance with POH/AFM data, runway slope and condition, wind, obstacles, aircraft configuration, and your operator’s procedures.

How to use this density altitude calculator

1. Enter the field elevation for the airport you are planning to use, and choose feet or meters to match the source you are reading.
2. Enter the outside air temperature from the current weather report, then select °C or °F so the calculator reads it correctly.
3. Enter the altimeter setting from METAR or ATIS, and select inHg or hPa to match that report exactly.
4. Compute the result, then compare it with your aircraft's performance chart and with a nearby cooler or warmer scenario if you want to see how fast density altitude can shift.

Formula note: how the density altitude estimate is built

This page uses the pressure-altitude-first method because it mirrors the way pilots usually reason about density altitude in preflight planning. The formula above turns field elevation and altimeter setting into pressure altitude, and the later steps convert that into an ISA temperature difference and a density altitude estimate. Keep the elevation, temperature, and pressure values in the units selected in the form; the calculator converts them before it computes the result.