Oxygen Saturation at Altitude Calculator
As altitude increases, barometric pressure falls and with it the partial pressure of inspired oxygen (PiO2). Lower PiO2 reduces the driving force for oxygen to cross the lung membrane into blood, causing arterial oxygen saturation (SpO2) to fall. This calculator estimates barometric pressure at altitude using the ICAO standard atmosphere equation, then estimates PiO2 and expected SpO2 for an unacclimatized person. Enter altitude in meters or feet to see the estimate.
Altitude oxygen formula
P(h) = 101.325 x (1 - 2.25577e-5 x h)^5.25588 kPa
PiO2 = (P - 6.27) x 0.2095
SpO2 estimated from oxyhemoglobin dissociation curve approximation
Where h is altitude in meters and P is barometric pressure in kPa. The value 6.27 kPa is saturated water vapor pressure at body temperature (37 degrees C). The fraction of oxygen in air is 0.2095 (20.95%). The SpO2 estimate uses a sigmoid approximation of the Hill equation for hemoglobin-oxygen binding.
Altitude and SpO2 reference table
- Sea level (0 m): SpO2 approximately 98-100%
- 1,500 m (4,921 ft): SpO2 approximately 95-97%
- 3,000 m (9,843 ft): SpO2 approximately 88-92%
- 4,500 m (14,764 ft): SpO2 approximately 82-86%
- 8,849 m (Everest summit): SpO2 approximately 54-70% (with acclimatization)
Oxygen saturation altitude calculator: frequently asked questions
Why does oxygen saturation decrease at altitude?
At higher altitudes, atmospheric pressure decreases. Since the fraction of oxygen in air (approximately 20.9%) stays constant, the partial pressure of inspired oxygen (PiO2) decreases proportionally with barometric pressure. Lower PiO2 means less oxygen drives diffusion across the lung membrane into the blood, resulting in lower arterial oxygen saturation (SpO2).
What is the standard atmosphere formula used?
This calculator uses the ICAO Standard Atmosphere (Doc 7488) barometric pressure formula: P = 101.325 x (1 - 2.25577e-5 x h)^5.25588 kPa, where h is altitude in meters. The partial pressure of inspired oxygen is then: PiO2 = (P - 6.27) x 0.2095, where 6.27 kPa is the saturated water vapor pressure at 37 degrees C.
What is a dangerously low oxygen saturation at altitude?
At sea level, normal SpO2 is 95-100%. At 3,000 m (9,843 ft), SpO2 typically drops to 88-92%. At 5,000 m (16,404 ft), it may be 80-85%. SpO2 below 85% can impair judgment and physical performance. SpO2 below 75% is life-threatening. Acute mountain sickness (AMS) typically begins above 2,500 m in unacclimatized individuals.
What is the Lake Louise Score for altitude sickness?
The Lake Louise Score (LLS) is a self-assessment questionnaire for acute mountain sickness (AMS), evaluated by the International Society for Mountain Medicine (ISMM). It assesses headache, gastrointestinal symptoms, fatigue, dizziness, and difficulty sleeping. A score of 3 or above after rapid ascent above 2,500 m suggests AMS. This calculator estimates the physiological oxygen effect; clinical assessment requires the full LLS.
How does acclimatization affect oxygen saturation at altitude?
Over days to weeks at altitude, the body acclimatizes by increasing breathing rate (hyperventilation), increasing red blood cell production (erythropoiesis), shifting the oxyhemoglobin dissociation curve, and increasing cardiac output. Acclimatized individuals typically have higher SpO2 at a given altitude than unacclimatized individuals. This calculator provides a baseline estimate for an unacclimatized person.
Official sources
- International Civil Aviation Organization (ICAO): Manual of the ICAO Standard Atmosphere, Doc 7488.
- Wilderness Medical Society: Wilderness Medical Society Practice Guidelines for Prevention and Treatment of Acute Altitude Illness.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.