Northern cardinals are medium-sized songbirds. Males are bright red except for a black mask on their face. Females are light brown or light greenish-brown, with reddish highlights and do not have a black mask (but parts of their face may be dark). Both males and females have thick, orange-red, cone-shaped bills, a long tail, and a distinctive crest of feathers on the top of their heads. Males are slightly larger than females. Males are 22.2 to 23.5 cm long whereas females are 20.9 to 21.6 cm long. The average weight of adult cardinals is 42 to 48 g. Immature cardinals are similar in appearance to females, but have a gray-black rather than orange-red bill.
There are 18 subspecies of Cardinalis cardinalis. The majority of these subspecies are distinguished based on the color of the face-mask in females. (Kielb, Swales, and Wolinski, 1992)