# Litres per minute (L/min, LPM)

WHO interim guidance of 4 April 2020 starts from oxygen flows in litres per minute (L/min) and sizes PSA plants in cubic metres per hour, converting L/min to L/h by multiplying by 60 and L/h to m³/h by dividing by 1,000.

The guidance, on oxygen sources and distribution for COVID-19 treatment centres, sizes PSA plants by output capacity in m³/h of oxygen gas. Its worked example is 75 severe COVID-19 patients at 10 L/min: 75 x 10 x 60 = 45,000 L/h, or 45 m³/h.

PATH and CHAI (July 2021) give the nominal flow of a conventional PSA plant as 8 to 2,500 litres per minute (LPM), or 0.5 to 150 Nm³/h, at 50 psi, and the typical maximum output of an oxygen concentrator as 3 to 12 LPM. HTM 02-01 (2026), the NHS England guidance, sets surgical air at a minimum of 700 kPa at the terminal unit at a flow of 350 L/min or 100 L/min. Plant capacities given in Nm³/h refer to reference conditions; see [normal cubic metre](https://library.ultracontrolo.com/glossary/normal-cubic-metre/).

The [ULTRAOX SC](https://library.ultracontrolo.com/products/ultraox-sc/) model table gives each model in both units, for example 5.3 l/min, or 0.318 m³/h, per unit for model 3.

## Sources

- [WHO, Oxygen sources and distribution for COVID-19 treatment centres, interim guidance (4 April 2020), conversion factors and Table 1](https://www.who.int/publications/i/item/oxygen-sources-and-distribution-for-covid-19-treatment-centres)
- [PATH and CHAI, Oxygen Generation and Storage: Pressure/Vacuum Swing Adsorption Plant (July 2021)](https://media.path.org/documents/O2_generation_and_storage_PSA_VSA_v1.pdf)
- [PATH and CHAI, Oxygen Generation and Storage: Oxygen Concentrator (July 2021)](https://media.path.org/documents/O2_generation_and_storage_oxygen_concentrators_v2.pdf)
- [HTM 02-01 (2026) Part A, paragraph 4.48 (NHS England)](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [ULTRAOX SC datasheet, p. 5](https://www.ultracontrolo.com/products/ultraox)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/litres-per-minute/