Cocker spaniels have thick coats that may become matted and require regular brushing. Unless you intend to show your dog, your cocker will look good and be perfectly happy with a short coat. After washing, drying and combing through the coat,we would suggest that 7mm (size 5) clipper blade would be suitable although in winter in a slighter longer cut may be required. You need to consider how you want the coat to look and whether you want a ‘Skirt’,which will require more ongoing grooming or an all over short cut. It may be worth the time to take your pet to a professional groomer and discuss the different types of cut so that you get exactly what you want with a professional finish.