101 altitudes — pressure, boiling point and oxygen

From sea level to 5000 m in 50-metre steps: the air pressure at that height, the temperature water boils at, and how much oxygen a single breath carries.

Heights people live at

Each is rounded to the nearest step on this table; published heights differ a little between surveys.

sea level0 m · 1013.25 hPa · 100 °C Seoul50 m · 1007.26 hPa · 99.83 °C Denver1600 m · 835.24 hPa · 94.58 °C Baekdu2750 m · 723.66 hPa · 90.66 °C Mexico City2250 m · 770.58 hPa · 92.36 °C Fuji3800 m · 632.64 hPa · 87.05 °C Lhasa3650 m · 645.04 hPa · 87.57 °C Mont Blanc4800 m · 554.79 hPa · 83.6 °C

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.

Altitude	Air pressure	Water boils at
0 m	1013.25 hPa	100 °C
500 m	954.61 hPa	98.31 °C
1000 m	898.75 hPa	96.62 °C
1500 m	845.56 hPa	94.92 °C
2000 m	794.95 hPa	93.22 °C
2500 m	746.83 hPa	91.51 °C
3000 m	701.09 hPa	89.8 °C
3500 m	657.64 hPa	88.09 °C
4000 m	616.4 hPa	86.37 °C
4500 m	577.28 hPa	84.64 °C
5000 m	540.2 hPa	82.91 °C

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.

Height alone fixes the pressure

The International Standard Atmosphere assumes the air cools 0.65 °C every 100 m. Feed that lapse rate into the barometric formula and height alone gives pressure — at 5000 m it is a little over half of sea level.

From 0 to 5000 m

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050 2100 2150 2200 2250 2300 2350 2400 2450 2500 2550 2600 2650 2700 2750 2800 2850 2900 2950 3000 3050 3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 3950 4000 4050 4100 4150 4200 4250 4300 4350 4400 4450 4500 4550 4600 4650 4700 4750 4800 4850 4900 4950 5000

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. Why does food come out underdone at altitude?

Because water never reaches 100 °C — it boils cooler and stays there. At 2000 m it boils at 93 °C, so the same minutes deliver less heat. A pressure cooker raises the pressure and undoes the problem.

Q. Is there really less oxygen up there?

The concentration is unchanged: even at 5000 m, 20.95% of the air is oxygen. But the pressure is about half, so a single breath brings roughly half the molecules.

Q. At what height does altitude sickness start?

Usually around 2500 m, and it varies enormously between people. This table shows pressure and oxygen; it says nothing about how a particular body will react.

Q. What altitude does an airliner cabin feel like?

Cabins are pressurised to roughly 1800–2400 m. That is why ears pop and a drink hits harder in flight.

Q. Where does pressure fall to half?

At about 5500 m. By 5000 m — the end of this table — it is already down to 53%.