For healthcare professionals
ROX Index Calculator
The ROX index (respiratory rate-oxygenation index) divides the SpO2/FiO2 ratio by the respiratory rate. In patients on high-flow nasal oxygen, it has been used to help predict whether the treatment will succeed or fail. This tool is written for clinicians and is not a diagnosis.
Bedside values
Use values measured at the same time on high-flow nasal oxygen. Nothing you enter leaves this page.
What you will see
The ROX index with the working, and how it compares with the published cut-offs at 2, 6 and 12 hours.
Educational only, not medical advice. Not a diagnosis. Decisions belong to the treating team.
Source
The formula as defined in the French oxygen therapy guidelines by Helms J and colleagues, Annals of Intensive Care 2024, and the cut-offs of Roca O and colleagues as reported by Goh KJ and colleagues, Journal of Intensive Care 2020. Both are open access (CC BY 4.0). The tests check the formula, each cut-off edge (a value equal to a failure cut-off is not below it; 4.88 counts as at or above 4.88) and that a value is never rounded onto a cut-off it is not on.
Validated in
Roca and colleagues studied patients with acute respiratory failure from pneumonia on high-flow nasal oxygen (as reported by Goh 2020). Goh 2020 tested these cut-offs in a prospective cohort of 145 patients on high-flow nasal oxygen, most with pneumonia and over half immunocompromised.
Limits
In the Goh 2020 cohort, the 4.88 cut-off had poor specificity (29 to 51%) for success and was not consistently linked with outcomes after adjustment. The ROX index does not appear as effective in immunocompromised patients and has not been studied enough in pre-hospital or emergency care; its reading depends on how the FiO2 is titrated (Helms 2024). Helms 2024 gives the failure thresholds as under 2.85 at 2 hours, under 3.5 at 6 hours or under 4.88 at 12 hours, which differs from the values reported by Goh 2020; this tool uses the Goh 2020 values (2.85, 3.47, 3.85).
The formula
ROX index = (SpO2 / FiO2) / respiratory rate, with SpO2 in % and FiO2 as a fraction (Helms 2024).
Worked example: SpO2 94% on FiO2 50% with a respiratory rate of 25 gives (94 / 0.50) / 25 = 7.52.
Published cut-offs
In patients with acute respiratory failure from pneumonia, Roca and colleagues reported a best cut-off of 4.88 at 2, 6 and 12 hours of high-flow nasal oxygen, and cut-offs of 2.85, 3.47 and 3.85 at 2, 6 and 12 hours for predicting failure (Goh 2020). The tool shows:
- At or above 4.88 at 2, 6 or 12 hours.
- Below 2.85 at 2 hours, below 3.47 at 6 hours or below 3.85 at 12 hours: the failure cut-offs.
- Between the two: neither reading.
When Goh and colleagues applied these cut-offs to their own cohort, 4.88 showed better sensitivity than their heart-rate version of the index but poor specificity (29 to 51%) for success (Goh 2020). The guidelines note that the index does not appear as effective in immunocompromised patients (Helms 2024).
Related tools
For an arterial blood gas, the PaO2/FiO2 ratio calculator gives the Berlin ARDS oxygenation band, and the A-a gradient calculator gives the alveolar-arterial gradient on room air. Other bedside scores are listed under For healthcare professionals.
Sources
- Helms J, Catoire P, Abensur Vuillaume L, Bannelier H, Douillet D, Dupuis C, et al. Oxygen therapy in acute hypoxemic respiratory failure: guidelines from the SRLF-SFMU consensus conference. Ann Intensive Care. 2024;14:140. doi:10.1186/s13613-024-01367-2. PMID 39235690. Open access (CC BY 4.0). Section on monitoring (ROX index definition and limits). pmc.ncbi.nlm.nih.gov/articles/PMC11377397/
- Goh KJ, Chai HZ, Ong TH, Sewa DW, Phua GC, Tan QL. Early prediction of high flow nasal cannula therapy outcomes using a modified ROX index incorporating heart rate. J Intensive Care. 2020;8:41. doi:10.1186/s40560-020-00458-z. PMID 32587703. Open access (CC BY 4.0). Results and Discussion (cut-offs of Roca et al. 2016 and 2019 at 2, 6 and 12 hours and their performance in this cohort). pmc.ncbi.nlm.nih.gov/articles/PMC7310118/
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.