Port Austin, Michigan · field elev 640 ft
Density Altitude at Grindstone Air Harbor (29C)
Grindstone Air Harbor sits at 640 ft, and even a typical July afternoon (78 °F) only lifts density altitude to about 2,031 ft — heat still trims performance, but the field rarely turns high-and-hot.
Typical density altitude by month
| Month | Avg temp °F | DA at avg temp | Afternoon high °F | DA on a typical afternoon |
|---|---|---|---|---|
| January | 22.9 | −1,663 ft | 29.0 | −1,230 ft |
| February | 22.7 | −1,678 ft | 30.2 | −1,146 ft |
| March | 30.6 | −1,117 ft | 38.2 | −589 ft |
| April | 41.9 | −335 ft | 50.8 | 266 ft |
| May | 53.9 | 472 ft | 63.5 | 1,101 ft |
| June | 63.7 | 1,114 ft | 73.0 | 1,710 ft |
| July | 68.9 | 1,449 ft | 78.1 | 2,031 ft |
| August | 67.7 | 1,372 ft | 76.7 | 1,944 ft |
| September | 61.0 | 939 ft | 70.5 | 1,551 ft |
| October | 50.1 | 219 ft | 58.1 | 749 ft |
| November | 38.8 | −548 ft | 45.3 | −104 ft |
| December | 29.0 | −1,230 ft | 34.7 | −831 ft |
▲ above 5,000 ft · ⚠ above 8,000 ft. These are planning references at standard pressure and dry air — afternoon humidity and low pressure both push the real number higher. Run today's values below.
Run today’s numbers for 29C
DENSITY ALTITUDE
Field elevation 640 ft — the air behaves like 2,025 ft.
- PRESSURE ALT
- 641 ft
- ISA DEVIATION
- —
- RULE-OF-THUMB DA
- —
- AIR DENSITY INDEX
- —
- AIR DENSITY
- —
- WATER · GRAINS/LB
- —
For training and reference · verify with official sources and your POH before flight · no tool on this site renders a go / no-go judgment
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Frequently asked questions
How high does density altitude get at 29C in summer?
On a typical July afternoon — around 78 °F at the nearest NOAA normals station — density altitude at Grindstone Air Harbor reaches roughly 2,031 ft at standard pressure. Hotter-than-normal days, low pressure, and humidity all push it higher, so run the day's actual numbers before flying.
What is the density altitude at 29C on an average day?
It swings with the seasons: from roughly −1,678 ft at the coldest month's average temperature to about 1,449 ft at the warmest month's — all from a constant field elevation of 640 ft. The month-by-month table above carries the full year.
What is the field elevation of Grindstone Air Harbor?
640 ft MSL, from the FAA NASR airport record (28-day cycle effective 2026-08-06). The identifier is 29C (FAA), in Port Austin, Michigan.