Density Altitude Calculator
The Number Behind "Hot, High, and Heavy"
Density altitude is one of the most repeated safety concepts in general aviation training, and for good reason: it's the single figure that explains why an aircraft performing normally at a cool sea-level airport can struggle to get airborne at a hot, high-elevation field on the same day. It represents pressure altitude corrected for non-standard temperature — effectively, the altitude the aircraft's engine and wings "feel" they're operating at, which can be thousands of feet higher than the airport's actual elevation.
The Formula
ISA Temperature at PA = 15 − 2 × (PA ÷ 1,000)
Density Altitude = PA + 120 × (OAT − ISA Temperature)
The core idea is the last line: for every degree Celsius the outside air temperature runs above the ISA-standard temperature for that altitude, density altitude increases by roughly 120 feet. On a hot day, that correction stacks up fast — a field at 5,000 feet elevation on a 35°C afternoon can present a density altitude well over 8,000 feet.
Where This Calculation Matters
- Takeoff performance — higher density altitude means thinner air, which means less lift, less propeller or engine thrust, and a longer takeoff roll than the same airport would require on a cooler day.
- Climb performance — rate of climb degrades directly with density altitude, sometimes to the point where obstacle clearance becomes marginal.
- High-elevation and summer operations — mountain and desert airstrips are the classic case, but even moderate-elevation airports can produce dangerous density altitudes on hot summer afternoons.
- Load planning — pilots often reduce fuel or passenger load specifically to compensate for a high density altitude day.
How Temperature Compounds Elevation
The table below illustrates density altitude at a representative 5,000-foot field elevation (standard altimeter setting) across a range of temperatures:
| Outside Air Temp | Density Altitude | Altitude Gain vs. Field Elevation |
|---|---|---|
| 5°C (ISA) | 5,000 ft | +0 ft |
| 15°C | 6,200 ft | +1,200 ft |
| 25°C | 7,400 ft | +2,400 ft |
| 35°C | 8,600 ft | +3,600 ft |
| 40°C | 9,200 ft | +4,200 ft |
How to Use This Calculator
- Enter the field elevation in feet, from the airport's published data.
- Enter the current altimeter setting in inches of mercury, from the latest METAR or ATIS.
- Enter the outside air temperature in degrees Celsius.
- Select Calculate to see pressure altitude, the ISA temperature reference for that altitude, and the resulting density altitude.
Related Calculations
Density altitude directly affects the numbers from Runway Length and Climb Rate planning — check both alongside this one when operating from a high or hot airport.