Health & Fitness
Alveolar-Arterial Oxygen Gradient Calculator
Calculate the A-a oxygen gradient and compare it with the age-expected value.
Preparing your result…
What this calculator does
Calculates Alveolar-Arterial Oxygen Gradient Calculator using the formula verified against the cited source.
What your result means
An estimate from the inputs you enter, within the scope stated below — not advice.
Formula
PAO₂ = FiO₂ × (Patm − 47) − pCO₂ ÷ 0.8; gradient = PAO₂ − PaO₂
The step-by-step working for your own numbers appears with the result above and in the PDF report.
Frequently asked questions
Symbols and assumptions
- Inputs
- The values entered in the fields above
- • Approximate alveolar PO2=FiO2×(barometric pressure−47)−PaCO2/0.8; A–a gradient=alveolar PO2−arterial PO2, all pressures mmHg and FiO2 a fraction.
Sources and review
Reviewed 2026-10-18 · Next review 2027-04-18
- • Assumes water-vapour pressure at 37°C, respiratory quotient 0.8 and a simplified alveolar-gas equation. Use actual altitude/barometric pressure; convert oxygen percent to fraction. Age does not enter the gradient calculation itself; a normal-age comparison requires a separately named reference and oxygen-condition scope.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Quick reference
| Scenario | Inspired oxygen (%) | Arterial pO₂ (mmHg) | Arterial pCO₂ (mmHg) | A-a gradient |
|---|---|---|---|---|
| Worked example | 21 | 80 | 40 | 19.73 mmHg |
| Half the amounts | 21 | 40 | 20 | 30.13 mmHg |
| Double the amounts | 42 | 160 | 80 | 56.26 mmHg |
Need the full picture? Get the detailed PDF report with charts, tables, formulas and working steps.
Reviewed 2026-10-18 · Next review 2027-04-18
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