Density Altitude Calculator
Density altitude and ISA from field elevation.
What it does
Density altitude tells wings the truth altimeters hide: hot thin air flies thousands of feet higher than the dial reads. A 5000 ft field at 25 C performs at 7400.
The tool above takes pressure altitude with outside air temperature in feet or meters. It returns density altitude with ISA temperature.
The default 5000 ft at 25 C gives 7400 ft against ISA 5 C. The sea level case at 30 C gives 1800, and 8000 ft at minus 5 gives 7520.
Aviation weather training defines DA as pressure altitude plus 120 feet per degree off ISA, lapsed at 2 C per thousand from 15. Pilot organizations drill the same rule before summer cross countries.
Thin air punishes climb, takeoff rolls, and engine power together. Lean per POH tables, respect density ceilings, and never let round dials overrule hot math.
How to use
- Pick feet or meters.
- Type pressure altitude.
- Type OAT in C.
- Read DA feet first.
- Read meters beside it.
- Read ISA last.
Formula
- PA
- Pressure altitude in ft.
- OAT
- Outside air temp in C.
- ISA
- Standard temp at PA in C.
Weather service aviation guidance teaches density altitude as pressure altitude corrected by 120 feet per degree off ISA. Pilot training organizations repeat the same rule with ISA lapsed at 2 C per 1000 ft from 15. Metric inputs convert meters at 3.28084 first.
Worked example
Example: hot high field
Imperial defaults: 5000 ft, 25 C OAT.
- Field: 5000 ft pressure altitude, 25 C outside.
- ISA: 15 minus 2 x 5 = 5 C.
- Gap: 25 minus 5 = 20 C hot.
- DA: 5000 + 120 x 20 = 7400 ft.
- Metric: 1524 m gives the same 7400.
- Tool shows 7,400 ft, 2256 m, ISA 5 C.
Reference table
| Field | ISA | DA |
|---|---|---|
| 5000 ft, 25 C | 5 C | 7400 ft |
| 0 ft, 30 C | 15 C | 1800 ft |
| 8000 ft, minus 5 C | -1 C | 7520 ft |
| 1524 m, 25 C | 5 C | 7400 ft |
Limits
- Rule of thumb, not tables.
- Humidity unread here.
- POH numbers rule dispatch.
- Turbos normalize partly.
Common mistakes
- Flying indicated altitude.
- Ignoring OAT entirely.
- Forgetting ISA lapse.
- Trusting cool morning math at noon.
- Skipping POH climb tables.
Try it yourself
Quick checks. Answers sit tucked under each question.
0 ft, 30 C?
ISA 15, DA 1800 ft: hot sea level still bites.
8000 ft, minus 5 C?
ISA minus 1, DA 7520 ft.
1524 m, 25 C?
1524 m mirrors 5000 ft: same 7400 ft.
Alt 99,999 ft?
Past service ceilings: enter pressure altitude in range.
Questions
Density altitude rule?
Pressure altitude plus 120 times OAT minus ISA. ISA falls 2 C per 1000 ft from 15.
Flyers care why?
Thin air cuts lift, thrust, and climb. Takeoffs stretch and service ceilings sink.
Hot days matter?
Yes, heat alone can add thousands: 5000 ft at 25 C density flies 7400.
Humidity included?
No, humidity trims further. The rule covers heat; moisture needs tables.
Below pressure altitude?
Yes, winter dense air can read thousands below the altimeter. Negative DA exists.
Go or no go?
No, this plans performance. Dispatch and POH numbers rule go decisions.