The invention relates to a sensor for determining a filling level of a liquid fellable into a container, having a light transmitter for transmitting at least one light pulse; having a receiver for receiving at least one reflected back light pulse, wherein the light pulse is at least partly reflect able at a liquid surface; having a control and evaluation unit for controlling the sensor and for evaluating the received back light pulse; and having a coupling and decoupling unit for coupling the light pulse into a liquid jet which can be introduced into the container and for decoupling the back light pulse to the receiver, wherein the control and evaluation unit is configured for determining a time difference between a transmission of the light pulse and a reception of the back light pulse to calculate a distance between the coupling and decoupling unit and the liquid surface.