P/F ratio calculator (PaO2/FiO2)
The P/F ratio measures oxygenation relative to the oxygen given and is widely used in intensive care.
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How to use it
- Enter pao2 and fio2.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
P/F = PaO2 (mmHg) ÷ FiO2 as a decimal. Berlin bands: over 200 to 300 mild, over 100 to 200 moderate, 100 or less severe.
Example
Inputs: PaO2 = 90 mmHg, FiO2 = 21 %. Result: P/F ratio: 429 mmHg; Berlin band: Above 300.
Limits and caveats
- The Berlin definition also needs PEEP of at least 5 cmH2O, chest imaging and timing; the ratio alone does not diagnose ARDS.
- An educational estimate that does not replace assessment by a doctor or pharmacist.
Questions about this tool
How do I enter FiO2?
As a percentage: 21 for room air and 100 for pure oxygen. The tool divides it by 100.
What is a normal value?
A healthy person breathing room air has about 400 to 500.
Why is it used in intensive care?
It ties oxygenation to the oxygen given, so patients can be tracked as ventilator settings change.