A breast pump device (1) comprises an expression kit (2) and a vacuum unit (3) configured to realize a pressure cycle in the expression kit (2). For the purpose of determining one or more milk expression characteristics such as total volume of expressed milk, the device (1) is equipped with an acoustic milk expression assessment system (6) including an acoustic sensor (61) and a processor (62) configured to process an acoustic signal received from the sensor (61) during operation of the device (1) when a receptacle (4) is used with the device (1) for receiving expressed milk. By recording sound during a pumping session, it is possible to determine a value of a time duration of a free fall of droplets of expressed milk from the expression kit (2) to the receptacle (4), which can be taken as a measure of a number of interesting milk expression characteristics.
