Grasmere, Idaho · field elev 5,144 ft
Density Altitude at Grasmere (U91)
Grasmere is a genuine high-and-hot field: from 5,144 ft of elevation, a typical July afternoon (86 °F) pushes density altitude to about 8,010 ft — the airplane performs like it is 2,866 ft above the field before the wheels roll.
Typical density altitude by month
| Month | Avg temp °F | DA at avg temp | Afternoon high °F | DA on a typical afternoon |
|---|---|---|---|---|
| January | 29.1 | 4,391 ft | 40.7 | 5,166 ft ▲ |
| February | 30.7 | 4,499 ft | 42.7 | 5,297 ft ▲ |
| March | 36.8 | 4,908 ft | 49.6 | 5,746 ft ▲ |
| April | 41.5 | 5,219 ft | 55.3 | 6,110 ft ▲ |
| May | 49.9 | 5,765 ft | 65.4 | 6,745 ft ▲ |
| June | 57.4 | 6,244 ft | 75.2 | 7,346 ft ▲ |
| July | 66.2 | 6,794 ft | 86.3 | 8,010 ft ⚠ |
| August | 65.1 | 6,726 ft | 85.0 | 7,933 ft ▲ |
| September | 56.9 | 6,212 ft | 76.5 | 7,424 ft ▲ |
| October | 45.6 | 5,487 ft | 62.3 | 6,552 ft ▲ |
| November | 35.2 | 4,801 ft | 48.5 | 5,675 ft ▲ |
| December | 27.8 | 4,303 ft | 39.9 | 5,113 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 U91
DENSITY ALTITUDE caution
Field elevation 5,144 ft — the air behaves like 7,993 ft.
- PRESSURE ALT
- 5,146 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
Nearby Idaho fields
- 3U0 — Murphy Hot Springs
Three Creek · elev 5,829 ft
- U89 — Glenns Ferry Municipal
Glenns Ferry · elev 2,536 ft
- U76 — Mountain Home Municipal
Mountain Home · elev 3,167 ft
- U03 — Buhl Municipal
Buhl · elev 3,663 ft
- 1U3 — Murphy
Murphy · elev 2,855 ft
- KGNG — Gooding Municipal
Gooding · elev 3,732 ft
- KTWF — Joslin Field/Magic Valley Regional
Twin Falls · elev 4,153 ft
- KJER — Jerome County
Jerome · elev 4,053 ft
Frequently asked questions
How high does density altitude get at U91 in summer?
On a typical July afternoon — around 86 °F at the nearest NOAA normals station — density altitude at Grasmere reaches roughly 8,010 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 U91 on an average day?
It swings with the seasons: from roughly 4,303 ft at the coldest month's average temperature to about 6,794 ft at the warmest month's — all from a constant field elevation of 5,144 ft. The month-by-month table above carries the full year.
What is the field elevation of Grasmere?
5,144 ft MSL, from the FAA NASR airport record (28-day cycle effective 2026-08-06). The identifier is U91 (FAA), in Grasmere, Idaho.