Altitude Oxygen Calculator
Effective oxygen and air pressure at any altitude.
About this tool
Enter an altitude in metres or feet, or pick a place. The tool shows the air pressure, the oxygen partial pressure, the inspired oxygen pressure in the lungs and the 'effective oxygen' percentage, plus a guide to the altitude zone.
Thinner air, less oxygen
Air is about 20.9% oxygen at every altitude, but air pressure falls as you climb, so each breath contains fewer oxygen molecules. What the body responds to is the oxygen partial pressure, 20.9% of total pressure, about 21.2 kPa at sea level. Expressing it as the oxygen percentage that would give the same partial pressure at sea level gives the effective oxygen figure used by altitude-training tents: at La Paz (3,640 m) air pressure is about 64% of sea level, equivalent to breathing 13.4% oxygen; at Everest Base Camp it's about 10.6%; on Everest's summit about 6.5% in the standard atmosphere. The lungs add water vapour, so the inspired oxygen pressure is a little lower still. Airliner cabins are typically pressurised to an equivalent of 1,800โ2,400 m. Altitude sickness becomes common above about 2,500 m, and gradual ascent is the key to acclimatising. Honest limits: real pressure depends on weather and latitude (it's higher near the equator, which makes Everest slightly easier than the model suggests), and individual tolerance varies. This is general information, not medical advice. The boiling point at altitude calculator and the hiking time calculator are related.
Frequently asked questions
Is there less oxygen at high altitude?
The percentage is the same (about 20.9%), but the air is thinner, so each breath holds less oxygen.
What is effective oxygen at altitude?
The sea-level oxygen percentage that would give the same oxygen partial pressure, about 13.4% at 3,640 m.
At what altitude does altitude sickness start?
It becomes common above about 2,500 m (8,000 ft), though some people are affected lower.
How much oxygen is at the top of Everest?
About a third of sea level: roughly 6.5 to 7% effective oxygen.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.