A pump having a drive unit with an electric motor, a hydraulic unit connected to the electric motor, and an integrated control unit operatively connected to the electric motor and configured for monitoring and controlling the pump. An integrated pressure sensor, connected to the control unit, has a fixed reference pressure. The control unit determines a liquid level of a liquid surrounding the pump based on a relation between an actual value of the pressure sensor and a reference value. A method for calibrating the pump comprises initiating pumping, continuing pumping until the liquid level is equal to a predetermined calibration level, determining the actual pressure value when the liquid level is equal to the predetermined calibration level, and calibrating the pump by setting a new reference pressure value corresponding to the actual pressure value.