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Free Density Altitude Calculator

Compute density altitude from field elevation, altimeter setting, and temperature. See pressure altitude, ISA deviation, and density altitude in your browser. No download, no account.

Airport elevation. Enter your pressure altitude here and leave the altimeter at 29.92 if you already have it.

Current altimeter setting. Defaults to standard (29.92) when left blank.

What density altitude is

Density altitude is pressure altitude corrected for non-standard temperature. Put simply, it is the altitude your aircraft and engine actually feel. Air density falls as temperature rises, so on a hot day the air is thinner than the standard atmosphere assumes and the aircraft behaves as if it were much higher than the field elevation on the chart. Density altitude is the single number that captures that effect, which is why aircraft performance charts are built around it rather than around raw field elevation.

Why density altitude matters

Less dense air means less power from the engine, less thrust from the propeller, and less lift from the wing. The practical results on a high density altitude day are:

  • Longer takeoff and landing rolls — the wing needs more true airspeed to fly, so you use more runway.
  • Reduced rate of climb — a normally aspirated engine makes less power, and the climb gradient suffers most where terrain matters most.
  • Higher true airspeed for a given indicated airspeed — approaches feel fast and floaty even though the airspeed indicator reads normal.

Hot-and-high operations — high-elevation airports on summer afternoons — are where density altitude bites hardest. It is routine for density altitude to sit thousands of feet above field elevation in those conditions, so always run the number and check it against your aircraft performance charts before departure.

How to calculate density altitude

The calculator works in two steps, using the same math as the density altitude tab in the Sky Duty E6B so the numbers stay consistent across the tools:

  1. Pressure altitude = field elevation + (29.92 − altimeter setting) × 1,000. This corrects field elevation to the standard 29.92 inHg datum.
  2. Density altitude = pressure altitude + 120 × (OAT − ISA temperature), where ISA temperature = 15 °C − 1.98 °C per 1,000 feet of pressure altitude.

If you already know your pressure altitude, enter it in the field-elevation box and leave the altimeter at the standard 29.92 — the result is identical to the E6B density altitude tab.

Worked example

A field elevation of 5,000 feet with the altimeter at 29.92 inHg gives a pressure altitude of 5,000 feet. On a 25 °C day, the ISA temperature at 5,000 feet is about 5.1 °C, so the air is roughly 19.9 °C warmer than standard. Density altitude works out to about 5,000 + 120 × 19.9 ≈ 7,400 feet. In other words, at a 5,000-foot field on a warm afternoon your aircraft performs as though it were departing from roughly 7,400 feet. Push the temperature higher or add elevation and the gap widens quickly.

The same tools, offline in the cockpit

This density altitude math is part of the full E6B built into the Sky Duty iOS app, alongside scheduling, logbook, maintenance, and expense tracking. All of it works offline, so you can run the numbers at a remote strip with no signal.

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FAQ

Frequently Asked Questions

What is density altitude?
Density altitude is pressure altitude corrected for non-standard temperature — the altitude the air density feels like to your aircraft and engine. On a hot day the air is thinner than standard, so the aircraft performs as if it were at a much higher altitude than the field elevation.
How do you calculate density altitude?
First find pressure altitude: field elevation plus (29.92 minus the altimeter setting) times 1,000. Then apply the standard rule of thumb: density altitude equals pressure altitude plus 120 feet for every degree Celsius the outside air temperature is above the ISA standard temperature at that altitude. ISA standard temperature is 15 degrees Celsius at sea level, dropping about 1.98 degrees Celsius per 1,000 feet. This calculator uses the same formula as the density altitude tab in the Sky Duty E6B.
What is the difference between pressure altitude and density altitude?
Pressure altitude is your altitude relative to the standard 29.92 inHg pressure datum — it accounts for barometric pressure but not temperature. Density altitude takes pressure altitude and corrects it for the actual temperature. On a standard day the two are equal; on a hot day density altitude is higher.
Why does density altitude matter for takeoff and climb performance?
High density altitude reduces engine power, propeller thrust, and wing lift because the air is less dense. That means longer takeoff rolls, reduced climb rate, and a higher true airspeed for the same indicated airspeed. Hot, high-elevation airports on summer afternoons can push density altitude thousands of feet above field elevation, which is why performance charts are built around it.
What is considered a high density altitude?
There is no single cutoff, but density altitude well above field elevation — often several thousand feet higher on hot days at high-elevation airports — signals degraded performance. Always check your aircraft performance charts for the computed density altitude rather than relying on a fixed number.
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