Calculate the PaO2/FiO2 (P/F) ratio from arterial oxygen and inspired oxygen fraction, with the Berlin ARDS severity bands.
Result
How to use this tool
Enter PaO2 in mmHg from the arterial blood gas.
Enter FiO2 as a percentage, from 21% (room air) to 100%.
Note whether PEEP is at least 5 cmH2O, as the Berlin bands assume.
Read the ratio and band, and discuss the full picture with the treating team.
Formula & worked example
PaO2 80 mmHg on FiO2 40% gives 80 / 0.40 = 200 mmHg, in the moderate ARDS range.
Limitations — read this before you rely on it
Screening aid only, not a diagnosis of ARDS. Bands assume PEEP of at least 5 cmH2O and the full Berlin criteria, which this tool does not assess. This tool is for education only and is not medical advice. Talk to a clinician about any result that worries you, and never change treatment because of a calculator result.
Frequently asked questions
Arterial oxygen pressure divided by the inspired oxygen fraction, used to grade how badly oxygen transfer is impaired.
Mild 200-300, moderate 100-200 and severe 100 or below, with PEEP of at least 5 cmH2O.
No. ARDS also needs acute onset, bilateral opacities and a cause not fully explained by cardiac failure.
The same PaO2 means something very different on room air (21%) than on 100% oxygen.
Convert first: 1 kPa is about 7.5 mmHg, then enter the mmHg value.