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Work out density altitude from pressure altitude and outside air temperature, plus the deviation from the ISA standard to gauge hot-day performance.

📘 How to Use

  1. Enter the pressure altitude (your altimeter reading set to 29.92 inHg)
  2. Enter the outside air temperature at your location
  3. Read the density altitude and the deviation from the ISA standard

Density Altitude Calculator

ft

The altimeter reading when set to 29.92 inHg (1013 hPa)

°C

The actual outside air temperature at the location

flight Results

Density altitude

— ft

—

Deviation from ISA standard

— °C
info

This is an estimation for general reference, not for flight planning; use official performance charts.

※ Uses the standard density altitude approximation of 120 ft per °C of ISA deviation

※ Humidity is not included; high humidity makes the real density altitude slightly higher

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Article

Density Altitude Calculator | Pressure Altitude + OAT to Density Altitude

Type in pressure altitude and outside air temperature, and get density altitude plus the deviation from the ISA standard. It is a quick way to gauge how much hot-day or high-elevation conditions are eating into your aircraft's performance, without reaching for an E6B.

💡 About this tool

Density altitude is the altitude in the standard atmosphere at which the air would have the same density as the air you are actually flying in. When the air gets thinner, your wings make less lift, your propeller bites less, and a normally aspirated engine makes less power. In short, the airplane "feels" like it is at a higher altitude than the altimeter shows.

On a hot afternoon or at a high-elevation field, density altitude can sit well above your pressure altitude, lengthening the takeoff roll and flattening the climb. A common rule of thumb is that takeoff distance grows roughly 10% for every 1,000 ft of density altitude above pressure altitude. Punching in the temperature and pressure altitude gives you a fast read on the day. This tool uses the pilot-training approximation of 120 ft of density altitude per 1°C of ISA deviation.

🧐 Frequently Asked Questions

What is the difference between pressure altitude and density altitude? Pressure altitude is what your altimeter shows with the Kollsman window set to 29.92 inHg (1013 hPa). Density altitude takes that and corrects for the difference between standard and actual temperature, expressing "how thin the air is" as an altitude. Hotter than standard means density altitude is higher than pressure altitude.

What does deviation from the ISA standard mean? The International Standard Atmosphere defines 15°C at sea level, decreasing about 1.98°C per 1,000 ft. The ISA deviation is the gap between that standard temperature for your altitude and the actual outside air temperature. A positive number means it is warmer than standard.

Why is there no humidity input? The widely used rule-of-thumb formula relies only on pressure altitude and temperature; it ignores humidity. High humidity pushes real density altitude slightly higher, so treat this result as a dry-air estimate.

Can I use this for flight planning? No. This is a general-reference estimate. For takeoff distance, climb rate, and go/no-go decisions, always use your aircraft's official performance charts in the POH.

📚 Why "high, hot, and humid" earns its reputation

Among bush and mountain pilots, the warning "high, hot, and humid" is shorthand for the days when performance quietly disappears. The classic example is a summer departure from a mountain strip: the field elevation has not changed, yet the airplane behaves as if the runway sits thousands of feet higher. That is why high-altitude operations often favor early-morning departures, when the cooler air is denser. Folding temperature into a single density-altitude number is what makes that intuition possible — it tells you, in plain feet, how high your airplane thinks it is today.