Partial Pressure of Oxygen at Altitude Calculator

Estimate oxygen pressure at elevation with humidity corrections. Compare dry, inspired, and alveolar values using practical chemistry calculations today.

Calculator Inputs

Plotly Graph

The chart compares dry oxygen pressure, inspired oxygen pressure, and estimated alveolar oxygen pressure from sea level to 10,000 meters.

Example Data Table

Altitude Barometric Pressure (kPa) Dry PO₂ (kPa) Inspired PO₂ (kPa) Estimated Alveolar PO₂ (kPa)
0 m 101.325 21.228 19.913 13.288
1,500 m 84.556 17.715 16.400 9.775
3,000 m 70.109 14.688 13.373 6.748
4,500 m 57.729 12.094 10.780 4.155
6,000 m 47.182 9.885 8.570 1.945

Formula Used

1) Barometric pressure at altitude
For the troposphere, pressure decreases with altitude using the barometric relation:
P = P₀ × (1 − Lh/T₀)^(gM/RL)

2) Dry oxygen partial pressure
PO₂(dry) = FIO₂ × P

3) Humid ambient oxygen pressure
PO₂(humid ambient) = FIO₂ × (P − PH₂O,ambient)

4) Inspired oxygen after airway humidification
PIO₂ = FIO₂ × (P − PH₂O,body)

5) Estimated alveolar oxygen
PAO₂ = PIO₂ − (PaCO₂ / RQ)

These formulas help estimate oxygen availability as elevation rises. The airway humidification adjustment is important because water vapor displaces part of the inspired gas pressure.

How to Use This Calculator

  1. Enter the altitude and choose meters or feet.
  2. Set sea-level pressure for your starting atmospheric conditions.
  3. Enter oxygen fraction. Standard air is about 20.95%.
  4. Provide ambient temperature and relative humidity.
  5. Enter body temperature, respiratory quotient, and PaCO₂.
  6. Click the calculate button to display results above the form.
  7. Review dry, humid, inspired, and alveolar oxygen pressures.
  8. Use the CSV or PDF buttons to export results.

FAQs

1) What does this calculator estimate?

It estimates oxygen partial pressure at altitude using atmospheric pressure, oxygen fraction, humidity, body vapor pressure, and an alveolar gas approximation.

2) Why does oxygen pressure drop with altitude?

The oxygen percentage in dry air stays nearly constant, but total atmospheric pressure decreases. Because partial pressure depends on total pressure, oxygen pressure falls as altitude rises.

3) What is the difference between dry and inspired oxygen pressure?

Dry oxygen pressure uses total barometric pressure only. Inspired oxygen pressure subtracts body water vapor pressure because inhaled air becomes fully humidified in the airways.

4) Why include humidity?

Humidity slightly changes ambient gas composition. It matters more for precise gas calculations, especially when comparing dry air values with real inhaled air conditions.

5) What does the alveolar oxygen value represent?

It estimates oxygen pressure in the alveoli after accounting for carbon dioxide and respiratory quotient. It is useful for physiology-based approximations, not diagnosis.

6) Which sea-level pressure should I enter?

Use 101.325 kPa for standard atmosphere. For more realism, enter your local sea-level adjusted pressure from meteorological observations or lab conditions.

7) Can I use this for oxygen-enriched mixtures?

Yes. Change the oxygen fraction input to evaluate enriched breathing gas conditions. The formulas scale the oxygen partial pressure directly from that fraction.

8) Is this calculator suitable for medical decisions?

No. It is an educational chemistry and gas-law tool. Medical interpretation requires clinical context, measurements, and guidance from qualified professionals.