The paper considers the solution of a problem of number of the moving connected with weighing of freights, reduction, consisting in development of the device for determination of the freight mass mounted directly on the dump truck. The operation of the suggested device is based on the principle of hydraulic sensors use. It consists of hydraulic sensors of the left and right longerons, hydraulic sensors system of high pressure oil pipelines, hydraulic ram’s high pressure oil pipeline, the oil pressure gauge thoriated in weight units, the three-running distributive tap, the hydraulic ram of the dump truck, the oil pump with the operation tap, an oil tank, low pressure oil pipeline, a return piping and the bilateral action valve. The hydraulic sensors of the left and right longerons are connected to a hydraulic ram high pressure oil pipeline in parallel via a three-running distributive tap and a bilateral action valve. The operation principle of hydraulic sensors of the device for weighing of freights is similar to the hydraulic ram operation.The dependences allowing determining the key parameters of the specified device such as the internal diameter of oil pipelines for a liquid supply to sensors of the left and right longerons according to the passed amount of working fluid, Reynolds number and pressure losses in all elements of the hydraulic system are presented.The suggested device in combination with the device for fixing of the transported freight mass can find broad practical application. Its use will allow reducing the transportations route and, therefore, increasing the efficiency and safety of transport and technological processes.