Boiling eggs at high altitude
At sea level water boils at 100 °C. Go up a mountain and it boils at a lower temperature, so the water around your egg is cooler and the egg takes longer to cook. At 4000 m the water boils at only 86.4 °C (187.5 °F).
Boiling point and egg times by altitude
For a medium egg (58 g) straight from the fridge, cooled in an ice bath afterwards.
| Altitude | Water boils at | Jammy | Hard-boiled |
|---|---|---|---|
| 0 m 0 ft | 100.0 °C (212.0 °F) | 8:36 | 11:20 |
| 500 m 1,640 ft | 98.3 °C (209.0 °F) | 8:50 | 11:45 |
| 1,000 m 3,280 ft | 96.6 °C (205.9 °F) | 9:06 | 12:11 |
| 1,500 m 4,920 ft | 94.9 °C (202.9 °F) | 9:22 | 12:40 |
| 2,000 m 6,560 ft | 93.2 °C (199.8 °F) | 9:40 | 13:13 |
| 2,500 m 8,200 ft | 91.5 °C (196.7 °F) | 9:59 | 13:50 |
| 3,000 m 9,840 ft | 89.8 °C (193.6 °F) | 10:20 | 14:33 |
| 4,000 m 13,120 ft | 86.4 °C (187.5 °F) | 11:08 | 16:21 |
Why water boils cooler up high
Water boils when its vapour pressure matches the pressure of the air above it. Higher up there is less air pressing down, so the water boils sooner, at a lower temperature. As a rule of thumb the boiling point drops by about 1 °C for every 300 m (1,000 ft) of altitude. The table uses the standard atmosphere and the Clausius–Clapeyron relation, the textbook way of calculating it.
A cooler pot means less heat flowing into the egg, so every style takes longer, and the effect grows with height. A hard-boiled egg is affected the most, because its yolk has to get closest to the temperature of the water.
Does salt or a lid help?
Not noticeably. A generous tablespoon of salt per litre raises the boiling point by only about 0.35 °C. A lid helps the water come back to the boil faster, but it does not make boiling water any hotter.
Open the calculator and choose Chef mode to enter your exact altitude.