For healthcare professionals
PaO2/FiO2 Ratio Calculator
The PaO2/FiO2 ratio (P/F ratio) divides the arterial oxygen pressure by the fraction of inspired oxygen. The Berlin definition of acute respiratory distress syndrome (ARDS) uses it to grade the oxygenation of ventilated patients, and the SOFA score uses it for its respiratory points. This tool is written for clinicians and is not a diagnosis.
Blood gas and oxygen
Use the PaO2 from an arterial blood gas and the FiO2 at the time it was drawn. Nothing you enter leaves this page.
What you will see
The PaO2/FiO2 ratio with the working, the Berlin oxygenation band and the SOFA respiratory points.
Educational only, not medical advice. Not a diagnosis. Decisions belong to the treating team.
Source
The Berlin definition oxygenation bands as printed in the French ARDS guidelines by Papazian L and colleagues, Annals of Intensive Care 2019, which cite the Berlin definition (Ranieri VM and colleagues, JAMA 2012); the SOFA respiratory points as printed in Table 1 of Lambden S and colleagues, Critical Care 2019. Both are open access (CC BY). The tests check the ratio, each band edge (100, 200 and 300 fall in the lower band) and that a value is never rounded onto a cut-off it is not on.
Validated in
The Berlin bands apply to patients who are ventilated with PEEP of at least 5 cm H2O. The SOFA score was designed for adult intensive care patients.
Limits
The ratio is only the oxygenation part of the Berlin definition: ARDS also needs onset within 7 days and bilateral opacities not fully explained by heart failure or fluid overload, which this tool does not check. In the SOFA table, 300, 200 and 100 count in the higher-scoring band only when the ratio is below them, while the Berlin bands include 300, 200 and 100 in the band below, so the two can differ at the edges.
The formula
PaO2/FiO2 ratio = PaO2 (mm Hg) / FiO2 (as a fraction, so 40% = 0.40).
Worked example: PaO2 80 mm Hg on FiO2 40% gives 80 / 0.40 = 200 mm Hg.
Berlin definition oxygenation bands
The Berlin definition describes ARDS as acute hypoxemia (PaO2/FiO2 of 300 mm Hg or less) in a ventilated patient with PEEP of at least 5 cm H2O, within 7 days of a known insult or new or worsening respiratory symptoms, with bilateral opacities not fully explained by heart failure or volume overload (Papazian 2019). It grades the ratio as (Papazian 2019):
- Mild: over 200 and up to 300 mm Hg.
- Moderate: over 100 and up to 200 mm Hg.
- Severe: 100 mm Hg or less.
SOFA respiratory points
The SOFA respiratory component gives 0 points for 400 mm Hg or more, 1 for under 400, 2 for under 300, 3 for under 200 with respiratory support and 4 for under 100 with respiratory support; without support the respiratory points stop at 2 (Lambden 2019). The tool counts ventilation with PEEP as respiratory support.
Related tools
For patients on high-flow nasal oxygen, the ROX index calculator uses SpO2/FiO2 and the respiratory rate. The A-a gradient calculator gives the alveolar-arterial oxygen gradient on room air. The SOFA score calculator adds the other five organ systems. Other bedside scores are listed under For healthcare professionals.
Sources
- Papazian L, Aubron C, Brochard L, Chiche JD, Combes A, Dreyfuss D, et al. Formal guidelines: management of acute respiratory distress syndrome. Ann Intensive Care. 2019;9:69. doi:10.1186/s13613-019-0540-9. PMID 31197492. Open access (CC BY 4.0). Introduction (Berlin definition and its PaO2/FiO2 bands, citing Ranieri VM et al. JAMA 2012;307:2526-2533). pmc.ncbi.nlm.nih.gov/articles/PMC6565761/
- Lambden S, Laterre PF, Levy MM, Francois B. The SOFA score: development, utility and challenges of accurate assessment in clinical trials. Crit Care. 2019;23:374. doi:10.1186/s13054-019-2663-7. PMID 31775846. Open access (CC BY). Table 1 (SOFA criteria) and the sections on development, calculation, the CNS component and defining sepsis. pmc.ncbi.nlm.nih.gov/articles/PMC6880479/
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-02. Spotted an error? See About.