A three-dimensional camera (130) of an automatic milking system records image data (Dimg) representing an outer surface of a teat (T1) of a dairy animal in three dimensions. Based on the image data (Dimg), a processing unit (140) performs a geometric analysis and calculates at least one size measure (W1, W2, L) of the teat (T1). A user interface (150) presents output data (DO [TCLR]) reflecting the size-related classification of the teat.