Oxygen cylinders come in a variety of sizes and configurations. When used by respiratory patients in the home health environment, they typically come in "e" size (small) and "h" size (very large). E sizes are 10.6 cm (4.25 inches) in diameter and 75 cm (30 inches) in height. H sizes are 22.5 cm (9 inches) in diameter and 137.5 cm (55 inches) high. Whatever the size of cylinder, it is important to know how to precisely calculate the amount of oxygen remaining in the tank. Fortunately, there is a simple formula available to the user to assist them with this calculation.

## Formula

Start by noting the amount of pressure remaining in your cylinder. Multiply this number by 3 if using an H cylinder or 0.28 if using an E cylinder. Divide the total by the number of litres per minute that your are using for your mask or nasal cannula. The resultant number is the duration in minutes that the cylinder will last.

## E cylinder example

As an example, a full E cylinder with 15,000 kpa (2,200 psi) of pressure being used to supply a 2 litre (3.5 pints) per minute nasal cannula of oxygen to a patient will last approximately 308 minutes.

## H cylinder example

A large H cylinder that is half full at 7 500 kpa (1,100 psi) pressure supplying an oxygen simple mask at 5 litres (9 pints) per minute will last approximately 660 minutes.