A breast pump arrangement having an expression kit with a milk flow sensor (200) is provided. The milk flow sensor (200) comprises a container (240) with a first end with a first opening (242) and a second end with a second opening (243). The second opening (243) allows an outflow of milk with a predefined outflow characteristics out of the container (241). The first opening (242) is larger than the second opening (243). A milk amount sensor (250) is provided to measure a height or volume of milk in the container. A calculating unit (260, 240) calculates a milk flow based on the height or volume measurements and the predefined outflow characteristic of the second opening (243).
