The Cavalier (along with the Pug) is perhaps the largest toy breed: though historically a lap dog, modern day fully-grown adults tend to fill a lap rather amply. It is nonetheless quite small for a spaniel, with fully-grown Cavaliers roughly comparable in size to adolescents of more conventional spaniel breeds. Breed standards call for a height between 29 and 33 cm (12–13 inches) with a proportionate weight between 4.5 and 8.5 kg (10 and 18 lb). Unlike most other spaniels, the Cavalier has a full-length tail well-feathered with long hair, which is typically carried aloft when walking.
The breed naturally grows a substantial silky coat of moderate length. Breed standards call for it to be free from curl, with a slight wave permissible. In adulthood, Cavaliers grow lengthy feathering on their ears, chest, legs, feet and tail; breed standards demand this be kept long, with the feathering on the feet cited as a particularly important feature of the breed.
A Cavalier's coat may be beautiful, but, because it can be long, it is very important to keep it well groomed. Daily brushing is recommended to ensure that the coat does not get matted and that foreign objects, such as grass and sticks, do not become entangled in the feathering. It also should not be bathed more than twice a week otherwise it may cause skin irritation. Fur on the feet and on the hind legs should be trimmed regularly. In hot climates, the ears should be thinned.
The breed has four recognized colors:
- Blenheim -pronounced 'Blenem'(rich chestnut on pearly white background)
- Tricolor (black and white with tan markings on cheeks, inside ears, resembling eyebrows, inside legs, and on underside of tail)
- Black and Tan (black with tan markings)
- Ruby (rich reddish-brown all over)
Parti-colors are the colors that include white: Blenheim and Tricolor. Whole-colors have no white: Black and Tan, and Ruby. The Blenheim is the most common color.