Oxygen at altitude calculator
This oxygen at altitude calculator shows how much oxygen a breath holds compared with sea level: at 8,000 ft the air pressure of the standard atmosphere is about 753 hPa, so each breath carries about 74 % of the oxygen at sea level – like breathing 15.6 % oxygen at the coast.
Source: NWS El Paso, Wxcalc „Pressure Altitude“: h = (1 − (P ÷ 1013.25)^0.190284) × 145366.45 ft, solved for pressure (read 10.10.2026). Updated: .
How it is calculated
Air pressure P = 1,013.25 × (1 − h ÷ 145,366.45)^(1 ÷ 0.190284) hPa with the altitude h in feet; oxygen per breath compared with sea level = P ÷ 1,013.25. The formula is the National Weather Service equation for pressure altitude, solved for the pressure. Dry air contains 20.95 % oxygen by volume (NASA Earth Fact Sheet); multiplied by the pressure this gives the oxygen partial pressure. The “equivalent” value is the oxygen share that would give the same partial pressure at sea level.
Oxygen level at altitude chart
| Altitude | Air pressure (inHg) | Oxygen vs. sea level | Equivalent O₂ at sea level |
|---|---|---|---|
| 2,000 ft | 27.82 | 93.0 % | 19.5 % |
| 5,000 ft | 24.89 | 83.2 % | 17.4 % |
| 8,000 ft | 22.22 | 74.3 % | 15.6 % |
| 10,000 ft | 20.57 | 68.8 % | 14.4 % |
| 12,000 ft | 19.03 | 63.6 % | 13.3 % |
| 14,000 ft | 17.57 | 58.7 % | 12.3 % |
| 18,000 ft | 14.94 | 49.9 % | 10.5 % |
| 20,000 ft | 13.75 | 45.9 % | 9.6 % |
1 inHg = 3.386389 kPa and 1 ft = 0.3048 m (NIST). The values are calculated for the standard atmosphere; real pressure varies with the weather. The formula describes the troposphere, which reaches up to 11,000 m (about 36,000 ft) in NASA’s atmosphere model, so the calculator stops there.
Altitude sickness
MedlinePlus describes acute mountain sickness as an illness that can affect climbers, hikers, skiers or travelers at high altitudes, usually above 8,000 feet (2,400 m), caused by the reduced air pressure and lower oxygen levels.
- Gradual ascent is the most important factor in prevention. MedlinePlus advises a day or two of rest for every 2,000 ft (600 m) of climb above 8,000 ft and sleeping at a lower altitude when possible.
- If symptoms appear, do not continue upward; the main treatment is to descend as rapidly and safely as possible.
- People with heart or lung disease should avoid high altitudes, according to MedlinePlus; ask a doctor before a trip to high altitude.
Plan the hike itself with the hiking time calculator; how cold it gets higher up shows the temperature at altitude calculator, and when water boils the boiling point altitude calculator.
Frequently asked questions
Is there less oxygen at high altitude?
Yes. The air pressure drops with altitude; MedlinePlus names reduced air pressure and lower oxygen levels as the cause of mountain sickness. With 20.95 % oxygen in dry air, a breath at 8,000 ft holds about 74 % of the oxygen at sea level.
What is the oxygen level at 10,000 feet?
About 68.8 % of the oxygen at sea level per breath – like breathing 14.4 % oxygen at the coast.
At what altitude does altitude sickness start?
MedlinePlus says acute mountain sickness usually occurs above 8,000 feet (2,400 m).
How is the oxygen partial pressure calculated?
Multiply the air pressure by 0.2095. At 8,000 ft: 753 hPa × 0.2095 ≈ 158 hPa, about 118 mmHg.
How fast should I climb?
MedlinePlus advises a day or two of rest for every 2,000 ft (600 m) of climb above 8,000 ft (2,400 m), and descending if symptoms develop.
Sources and legal basis
- NWS El Paso, Wxcalc „Pressure Altitude“: h = (1 − (P ÷ 1013.25)^0.190284) × 145366.45 ft, solved for pressure (read 10.10.2026)
- NASA Glenn Research Center, Earth Atmosphere Model – Metric Units: troposphere up to 11,000 m, different curves above – calculation therefore limited to 11,000 m (36,089 ft) (read 10.10.2026)
- NASA NSSDCA, Earth Fact Sheet: dry air 20.95 % oxygen by volume (read 10.10.2026)
- MedlinePlus (U.S. National Library of Medicine), “Acute mountain sickness”: mostly above 8000 ft (2400 m), low air pressure and oxygen, for every 2000 ft (600 m) of ascent above 2400 m one to two rest days, descend if symptoms occur (read 10.10.2026)
- NIST Special Publication 811, Appendix B.8: foot = 0.3048 m, mmHg = 133.3224 Pa, inHg = 3.386389 kPa (read 10.10.2026)
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