Altitude oxygen calculator
An oximeter that reads 98% at home commonly reads around 90% on a first night in a mountain town, because the air holds less oxygen. Enter an elevation or pick a place to see the range reported for healthy visitors. Add your own reading to compare.
How the numbers are worked out
- Air pressure comes from the International Standard Atmosphere. Real pressure shifts a few percent with the weather.
- Oxygen reaching the lungs is 21% of that pressure, after the airways add water vapour.
- Expected SpO2 is not a formula. It is the range reported for healthy adults from low altitude, at rest, in their first day or two at each height.
What changes as you acclimatise
You breathe faster and deeper within hours, and resting SpO2 at a given height usually climbs a few points over the first week. If a reading stays flat or falls, or you have headache, nausea or breathlessness at rest, stop ascending and get medical advice.
Why nights matter more than spot checks
Above about 2,500 m most people develop periodic breathing in sleep, so the lowest oxygen of a trip is usually at night. A daytime spot check cannot see it. Record a night and load it into the free session viewer to see how much of it sat below 90%. The blog covers what to expect night by night.
Not a medical device. Does not diagnose, treat or prevent any condition. Discuss results and changes with a clinician.