P/F Ratio Calculator

P/F Ratio Calculator for Pulmonology. The displayed Berlin oxygenation bands place exactly 100 in severe, 200 in moderate and 300 in mild. These are conditional bands, not ARDS diagnoses; respiratory support, timing, imaging and cause must also satisfy the chosen definition.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

P/F = arterial PaO2 / FiO2 expressed as a fraction. Exactly 100 is in the severe oxygenation band, 200 moderate, and 300 mild under Berlin definitions.

When to use this calculator

Use to quantify oxygenation with a reliable arterial sample and inspired oxygen estimate. Applying an ARDS severity label additionally requires the other criteria of the selected definition and its respiratory-support conditions.

Inputs used

  • PaO2 (mmHg)
  • Inspired oxygen (%)

Clinical interpretation

The displayed Berlin oxygenation bands place exactly 100 in severe, 200 in moderate and 300 in mild. These are conditional bands, not ARDS diagnoses; respiratory support, timing, imaging and cause must also satisfy the chosen definition.

Worked example

Fictional teaching case. PaO2 (mmHg): 72; Inspired oxygen (%): 60. Result: 120 mmHg. Moderate Berlin oxygenation band. A P/F ratio alone does not diagnose ARDS. Berlin classification additionally requires positive-pressure support, timing, bilateral imaging changes and exclusion of a primarily hydrostatic cause.

Limitations and safety notes

FiO2 from low-flow oxygen devices is uncertain. Berlin bands assume PEEP/CPAP at least 5 cm H2O and other clinical criteria; newer global ARDS definitions include additional settings that are not diagnosed here.

Frequently asked questions

Is P/F 200 mild ARDS?

At exactly 200, the Berlin oxygenation band is moderate, but ARDS still requires the remaining diagnostic and support criteria.

What can change the meaning of this result?

FiO2 from low-flow oxygen devices is uncertain. Berlin bands assume PEEP/CPAP at least 5 cm H2O and other clinical criteria; newer global ARDS definitions include additional settings that are not diagnosed here.

References

  • Original Berlin ARDS definition and inclusive oxygenation thresholds. https://pubmed.ncbi.nlm.nih.gov/22797452/
  • Global ARDS definition broadens settings; ratio alone remains insufficient. https://doi.org/10.1164/rccm.202303-0558WS

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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