A hydraulic mass-determining unit arranged for determining the mass of a load held by a hydraulic fluid system, the mass-determining unit is adapted to be connected to a hydraulic pump at a first fluid connection and a hydraulic actuator of a lifting device at a second fluid connection, the mass-determining unit comprises a first pipe arranged for connecting the first fluid connection and the second fluid connection, and at least one pressure sensor arranged to measure the pressure in the first pipe, wherein the mass-determining unit further comprises a flow regulator with a pressure compensator, where the flow regulator is serially connected to the first pipe to regulate the flow in the first pipe, and one of a pressure switch arranged for measuring the pressure difference over the flow regulator, and for sending a signal to the pressure sensor to measure the pressure in the first pipe when the pressure difference is above a preset value, or a magnetic field switch that comprises a magnet attached to the pressure compensator and a detecting unit arranged for detecting whether the magnet and the pressure compensator are in an initial position, and for sending a signal to the pressure sensor to measure the pressure in the first pipe when the detecting unit detects that the pressure compensator is not in the initial position, and a processor for based on the measured pressure in the first pipe by the pressure sensor calculating a mass of the load.