A modular ultrasonic flow meter including a substantially watertight meter housing connected to a flow tube; a measurement printed circuit board including a measurement circuit communicating with one or more ultrasonic transducers, arranged in the meter housing for transmitting and receiving ultrasonic signals; and a self-contained power supply. The ultrasonic flow meter further includes a control module comprising a module housing connected with a main printed circuit board including a central processing unit, a memory circuit and a communication circuit, and a power- and communication connection is provided between the main printed circuit board of the control module and the measurement printed circuit board whereby the self-contained power supply may power the main printed circuit board and the measurement printed circuit board.