A bison has a shaggy, long, dark-brown winter coat, and a lighter-weight, lighter-brown summer coat. As is typical in ungulates, the male bison is slightly larger than the female and, in some cases, can be considerably heavier. Plains bison are often in the smaller range of sizes, and wood bison in the larger range. Head-and-body lengths range from 2 to 3.5 m (6.6 to 11.5 ft) long, the tail adding 30 to 91 cm (12 to 36 in). Shoulder heights in the species can range from 152 to 186 cm (60 to 73 in). Weights can range from 318 to 1,000 kg (701 to 2,205 lb) Typical weight ranges in the species were reported as 460 to 988 kg (1,014 to 2,178 lb) in males and 360 to 544 kg (794 to 1,199 lb) in females, the lowest weights probably representing typical weight around the age of sexual maturity at 2 to 3 years of age.
Mature bulls tend to be considerably larger than cows. Cow weights have had reported medians of 450 to 495 kg (992 to 1,091 lb), with one small sample averaging 479 kg (1,056 lb), whereas bulls may reportedly weigh a median of 730 kg (1,610 lb) with an average from a small sample of 765 kg (1,687 lb). The heaviest wild bull ever recorded weighed 1,270 kg (2,800 lb). When raised in captivity and farmed for meat, the bison can grow unnaturally heavy and the largest semidomestic bison weighed 1,724 kg (3,801 lb).
The heads and forequarters are massive, and both sexes have short, curved horns that can grow up to 2 ft (61 cm) long, which they use in fighting for status within the herd and for defense.