P/F Ratio (PaO₂/FiO₂) Calculator
Calculate the P/F ratio for ARDS screening and oxygenation assessment.
Understanding this tool
Why nurses use it
The P/F ratio (PaO₂/FiO₂) quantifies oxygenation severity — central to ARDS Berlin definition and ICU trending.
When to use it
Use with arterial blood gas PaO₂ and documented FiO₂ (decimal or %). Not for SpO₂ substitution.
Calculate
How to use this calculator
- Enter PaO₂ from ABG (mmHg).
- Enter FiO₂ as percentage (e.g. 40 for 40%).
- Interpret with PEEP, imaging, and timing criteria for ARDS.
How the calculation works
P/F = PaO₂ ÷ FiO₂ (as decimal). Lower ratios indicate worse oxygenation: mild <300, moderate <200, severe <100 mmHg.
Formula used by this tool — verify units before applying at the bedside.
Worked example
Limitations & clinical notes
- Berlin definition also requires timing, imaging, and exclusion of cardiac failure.
- Use ABG PaO₂ — pulse oximetry is not a substitute.
References
Key sources: Berlin ARDS definition.
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Disclaimer: This calculator is for educational and bedside double-check purposes only. It does not replace institutional protocols, prescriber orders, pharmacist verification, or clinical judgment. Always follow your local policies — especially for high-risk medications, infusions, pediatrics, and critical care. If the patient is acutely unwell, escalate immediately rather than relying on any calculator output.