The present invention relates to an oxygen breathing device, in particular for providing oxygen to passengers or crew of an aircraft, the device comprising an oxygen source for providing pressurized oxygen, a valve connected to the oxygen source via a pressure line, a control unit for controlling said valve, and at least one nozzle for dispensing the oxygen passing through said valve. In particular, the present invention relates to an oxygen breathing device comprising a measuring unit for determining the mass flow rate of oxygen passing through said nozzle. Furthermore, the invention relates to a method for supplying oxygen to a person, in particular a flight passenger, using an oxygen breathing device.