0 m above sea level — 1013.25 hPa, water boils at 100 °C
At 0 m the pressure is 1013.25 hPa, 100% of sea level. Water boils at 100 °C and the oxygen pressure is 212.28 hPa.
- Air pressure
- 1013.25 hPa (100%)
- Feet
- 0 ft
- Standard temperature
- 15 °C
- Oxygen pressure
- 212.28 hPa (100%)
- Cooking time
- ×1
Water does not always boil at 100
Water boils when its vapour pressure matches the air pressing on it. Higher up there is less air pressing, so it boils cooler — and cooks slower for the same reason.
It is not the concentration that thins
Oxygen still makes up 20.95% of the air at 5000 m, exactly as at sea level. What falls is the pressure, so each breath brings fewer molecules — that quantity is the oxygen partial pressure.
Nearby heights
Heights people live at
Each is rounded to the nearest step on this table; published heights differ a little between surveys.
How to read this
- Pressure comes from height through the standard atmosphere formula.
- Temperature is taken to fall 0.65 °C every 100 m.
- The boiling point follows from that pressure — lower pressure, cooler boil.
- Oxygen stays at 20.95% everywhere; what drops is its partial pressure.
These assume the International Standard Atmosphere. Real pressure swings by tens of hectopascals with the weather, and real temperature varies far more with season and terrain.
Frequently asked questions
Q. What is the air pressure at 0 m?
1013.25 hPa — 100% of the 1013.25 hPa at sea level.
Q. What does water boil at here?
100 °C, which is why boiling food takes about 1 times as long.
Q. How much oxygen does a breath carry?
The oxygen pressure is 212.28 hPa, 100% of sea level. The concentration is still 20.95%.
Q. And the standard temperature?
15 °C. Real temperature swings widely with season and weather.