Austin, Texas · field elev 595 ft
Density Altitude at San Marcos Regional (KHYI)
San Marcos Regional sits at 595 ft, and even a typical August afternoon (97 °F) only lifts density altitude to about 3,124 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 | 50.6 | 197 ft | 62.3 | 968 ft |
| February | 54.5 | 456 ft | 66.6 | 1,246 ft |
| March | 61.3 | 903 ft | 73.1 | 1,661 ft |
| April | 68.0 | 1,336 ft | 79.8 | 2,083 ft |
| May | 75.5 | 1,813 ft | 86.2 | 2,479 ft |
| June | 82.1 | 2,226 ft | 92.4 | 2,858 ft |
| July | 84.5 | 2,375 ft | 95.7 | 3,057 ft |
| August | 85.2 | 2,418 ft | 96.8 | 3,124 ft |
| September | 79.5 | 2,064 ft | 90.5 | 2,743 ft |
| October | 70.1 | 1,471 ft | 82.1 | 2,226 ft |
| November | 59.9 | 812 ft | 71.5 | 1,560 ft |
| December | 52.2 | 303 ft | 63.7 | 1,059 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 KHYI
DENSITY ALTITUDE
Field elevation 595 ft — the air behaves like 3,136 ft.
- PRESSURE ALT
- 596 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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- KAUS — Austin-Bergstrom International
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- 3R9 — Lakeway Airpark
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- 1T7 — Kestrel Airpark
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- T20 — Roger M Dreyer Meml
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- 1T8 — Bulverde Airpark
San Antonio · elev 1,088 ft
Frequently asked questions
How high does density altitude get at KHYI in summer?
On a typical August afternoon — around 97 °F at the nearest NOAA normals station — density altitude at San Marcos Regional reaches roughly 3,124 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 KHYI on an average day?
It swings with the seasons: from roughly 197 ft at the coldest month's average temperature to about 2,418 ft at the warmest month's — all from a constant field elevation of 595 ft. The month-by-month table above carries the full year.
What is the field elevation of San Marcos Regional?
595 ft MSL, from the FAA NASR airport record (28-day cycle effective 2026-08-06). The identifier is KHYI (ICAO) / HYI (FAA), in Austin, Texas.