P/F ratio, oxygenation index, and escalation context
P/F Ratio Calculator & Oxygenation Index
Calculate the P/F ratio and oxygenation index to assess oxygenation failure, frame ARDS severity, and understand when a patient may be approaching ECMO-level respiratory failure.
Built for respiratory therapists, ICU clinicians, and students who want a fast bedside framework for interpreting oxygenation. Pair it with our P/F Ratio guide, A–a Gradient calculator, Causes of Hypoxemia, and Mastering ABG Analysis.
Calculator inputs
Required for oxygenation index calculation.
Leave blank when MAP is not measured, including for HFNC.
Enter as decimal (e.g. 0.5 for 50%).
What this calculator tells you
P/F ratio
The PaO₂/FiO₂ ratio helps grade oxygenation severity and is a core part of ARDS classification.
Oxygenation index
The oxygenation index adds mean airway pressure, making it more useful when ventilator support intensity matters.
Results
Quick interpretation guide
P/F ratio cutoffs
- Normal: > 300
- Mild ARDS oxygenation range: 201–300
- Moderate ARDS oxygenation range: 101–200
- Severe ARDS oxygenation range: ≤ 100
OI checkpoints
- Lower values suggest milder oxygenation impairment
- OI ≥ 25 suggests severe oxygenation failure
- OI ≥ 40 raises concern for ECMO-level severity
This tool works best when combined with broader gas-exchange assessment using the causes of hypoxemia framework and the A–a gradient.