# How do you estimate a hospital's oxygen demand?

**How do you estimate a hospital's oxygen demand before sizing a PSA plant?**

One way to estimate a hospital's oxygen demand is to count the patients expected to need oxygen, multiply each group by its average flow in litres per minute, and convert the total to m³/h, the unit PSA plants are sized in. WHO used this method in its 2020 interim guidance for COVID-19 treatment centres.

## WHO's COVID-19 calculation

In its interim guidance Oxygen sources and distribution for COVID-19 treatment centres (4 April 2020), WHO starts from the anticipated case load, splits the patients by severity and applies an average oxygen flow per patient. The total in litres per minute is multiplied by 60 to give litres per hour and divided by 1,000 to give m³/h. WHO's worked example is a hypothetical 100-bed COVID-19 treatment facility:

| Severity | Patients | Average flow per patient | Oxygen needed |
|---|---|---|---|
| Severe | 75 | 10 L/min | 45 m³/h |
| Critical | 25 | 30 L/min | 45 m³/h |
| Total |  |  | 90 m³/h |

WHO adds three cautions. The example is based on a patient count, while typical quantification would be based on the equipment available. For critical patients, the flow is only the oxygen portion of the gas, averaged over the time on assisted ventilation. Needs should be reassessed once the equipment has been commissioned. These flows describe COVID-19 patients; they are not a general figure per hospital bed.

## Adjusting the estimate to a real hospital

- Do not size on today's consumption alone. Global Fund sustainability guidance says need should not be estimated by current demand, and that oxygen production should be compared with consumption every year.
- Ask the clinicians. Open Critical Care advises starting with the clinicians and their usual patient mix, and notes that consumption may rise as pulse oximeters are used more to diagnose and treat patients.
- Allow for the plant's own use. HTM 02-01 (2026) notes that PSA regeneration uses a proportion of the product gas, and that this should be taken into account when sizing.
- Fix the purity. Output depends on purity: the Global Fund purity note (2024) gives the example of equipment producing 20 Nm³/h at 93% (±3%) but 18 Nm³/h at 95% (±1%).
- Add cylinder filling. If the plant will also fill cylinders, the number and size of cylinders to fill per day are part of the demand.

To size an ULTRAOX plant, Ultra Controlo needs the oxygen flow required in m³/h or, for cylinder filling, the size and number of cylinders to fill per day. ULTRAOX ST models range from 0.32 to 164 m³/h per unit, and plants are modular, so capacity can be added later. See also [what capacities ULTRAOX plants cover](https://library.ultracontrolo.com/answers/ultraox-capacity-range/).

### How many litres per minute of oxygen per bed?

There is no single figure. WHO's 2020 example uses 10 L/min per severe and 30 L/min per critical COVID-19 patient, which describes those patients, not every bed.

### How do you convert L/min to m³/h?

Multiply by 60 to get litres per hour, then divide by 1,000 to get m³/h, as in WHO's 2020 guidance.

## Sources

- [WHO, Oxygen sources and distribution for COVID-19 treatment centres, interim guidance (4 April 2020), Table 1](https://www.who.int/publications/i/item/oxygen-sources-and-distribution-for-covid-19-treatment-centres)
- [Global Fund / Build Health International, Overview: Sustainability Guidance for PSA Oxygen Plants (22 August 2024)](https://resources.theglobalfund.org/media/bwrp43cm/cr_c19rm-psa-oxygen-plant-sustainability_overview_en.pdf)
- [Open Critical Care, Oxygen FAQ: How to calculate total demand of oxygen for a health care facility?](https://opencriticalcare.org/faq/how-to-calculate-total-demand-of-oxygen-for-a-health-care-facility/)
- [NHS England, HTM 02-01 Part A (2026), paragraph 6.110](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)
- [Global Fund / Build Health International, Briefing Note: PSA Plant Oxygen Purity (3 April 2024)](https://resources.theglobalfund.org/media/lenpqaoa/cr_c19rm-psa-oxygen-purity_technical-briefing-note_en.pdf)
- [Ultra Controlo, Medical gas answers: What capacities do ULTRAOX plants cover?](https://www.ultracontrolo.com/medical-gas-answers#ultraox-capacity-range)
- [ULTRAOX ST datasheet, p. 5 (model table)](https://www.ultracontrolo.com/products/ultraox-st)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-to-estimate-hospital-oxygen-demand/