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Berlin ARDS Criteria Calculator

Enter PaO₂ and FiO₂ to get the PaO₂/FiO₂ ratio and ARDS severity.

How it is calculated

The tool divides the arterial oxygen partial pressure by the fraction of inspired oxygen: ratio = PaO₂ ÷ FiO₂. PaO₂ is entered in mmHg and FiO₂ as a fraction between 0 and 1 (room air is 0.21, not 21), so the ratio is also in mmHg. The ratio is shown as a whole number but grouped on its exact value: above 300 gives "No ARDS", above 200 up to 300 gives Mild, above 100 up to 200 gives Moderate, and 100 or below gives Severe. A ratio of exactly 300 therefore counts as mild and exactly 200 as moderate, while 300.4 shows as 300 and counts as no ARDS. Only the ratio is used. The tool cannot check the other Berlin conditions: timing of onset, chest imaging, the cause of the oedema, or whether the PEEP was at least 5 cmH₂O. A PaO₂ or FiO₂ of 0 or less, or an FiO₂ above 1, gives no result.

Worked example

A ventilated patient has a PaO₂ of 150 mmHg on an FiO₂ of 0.60. The ratio is 150 ÷ 0.60 = 250. That is above 200 and not above 300, so the tool reports Mild ARDS. If the same PaO₂ were measured on an FiO₂ of 0.75, the ratio would drop to 200 and the label would change to Moderate. The classification is only meaningful together with the other Berlin criteria, which the clinician must assess.

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Common mistakes

  • Entering FiO₂ as a percentage, such as 60 or 21. The field expects a fraction (0.60 or 0.21); a value above 1 returns no result.
  • Entering PaO₂ in kPa instead of mmHg. The cut-offs are in mmHg, so a kPa value gives a ratio roughly 7.5 times too small.
  • Using SpO₂ (pulse oximeter saturation) in place of PaO₂ from an arterial blood gas. The ratio needs the partial pressure.
  • Reading "No ARDS" as a clinical exclusion. It only means the ratio is above 300; the diagnosis depends on onset, imaging and PEEP, none of which this tool checks.
  • Mixing up the boundaries: a ratio of exactly 200 is moderate here, not mild, and exactly 300 is mild, not normal.

Sources

About this calculator

The Berlin Definition (published in JAMA, 2012) is the current clinical standard for diagnosing and grading acute respiratory distress syndrome (ARDS). It classifies severity purely by the PaO₂/FiO₂ ratio — arterial oxygen partial pressure divided by the fraction of inspired oxygen, measured with at least 5 cmH₂O of PEEP — into mild (>200–300 mmHg), moderate (>100–200 mmHg), and severe (≤100 mmHg), alongside onset within one week and bilateral opacities on chest imaging not fully explained by heart failure.

Intensivists, pulmonologists, and ICU nursing staff use this ratio at the bedside to grade how impaired a ventilated patient's oxygen exchange is, which in turn guides decisions on PEEP settings, prone positioning, and the intensity of mechanical ventilation support.

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  • Editorial team

    Be careful at the edges of a band. The tool shows the ratio as a whole number but groups it using the exact value, so a PaO2 of 150.2 on an FiO2 of 0.5 displays 300 and is still read as above the mild band. It also cannot see PEEP, timing or imaging, which the definition requires, so the label is only a ratio grade. For borderline readings, the treating team decides. Which part of the definition do you find hardest to apply?

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