For oxygen the following is valid:
- 1 nm3 = 1.311 kg
- 1 kg = 0.763 nm3
- 1 bar = 14.5 psi
- 1 nm3 = 35.3 ft3
- 1 kg = 2.2 lbs
The gas capacity of a cylinder can calculated in two different ways. The most simple method is the water capacity of the cylinder (in litres) multipled by the actual pressure (in bar); the result is the capacity in litres. Although a simple method it is not the most accurate method. A better but much more complex method will give a more accurate value for the gas capacity; it will take the compressability of the gas at both 1 bar and at the actual pressure in consideration and all based on 15 degrees C. The result is often quoted as normal litres or normal cubic metres (nm3). For oxygen the more accurate method will give a slightly higher value as compared to the simple method (6.4 m3 versus 6 nm3).