The invention relates to a method and a device for quantitively determining the number and size of particulate components contained in a medium flowing along a flow channel, wherein ultrasonic waves are coupled into the flowing medium, which are reflected at least partially on the particulate components and the reflected ultrasonic wave portions of which are detected in the form of ultrasonic timesignals, on which the quantitive determining is based. The invention is characterised by the following method steps: coupling the ultrasonic waves into the flowing medium in such a way that at leastone portion of the coupled-in ultrasonic waves is reflected on a wall region of the flow channel bordering the flow medium or a reflector introduced within the flow channel, via which an echo-ultrasonic time signal that can be associated with the wall region or the reflector is generated; determining at least one amplitude threshold value function which establishes an amplitude threshold value foreach detected ultrasonic time signal, taking into consideration at least the echo-ultrasonic time signal; detecting amplitude values associated with the individual ultrasonic time signals, which areeach greater than an amplitude threshold value established for each ultrasonic time signal; and assigning the detected amplitude values to values describing the size and number of the particulate components.