The number of liters of oxygen in the cylinder depends on the size of the cylinder, i.e. on how much space the oxygen occupies inside the cylinder. Usually the capacity of the cylinder is written on the cylinder in the form of a tattoo. A standard size cylinder has a capacity of 1.36 m3 to 1.4 m3 which when converted to liters is 1360 liters to 1400 liters. What the Flowmeter shows is the pressure which is always 2000.