How Big Is a Bison? Weight and Height of America's Giant

Bison size at a glance

The figures below are for the American bison (Bison bison), using wild adults. Individual animals vary a lot with age, season, food supply and subspecies.

Yellowstone National Park, home to the largest bison herd on public land in the US, uses simple round figures: bulls up to about 2,000 lb (900 kg) and cows about 1,000 lb (450–500 kg).

How big are bison bulls compared with cows?

Bison show strong sexual dimorphism, which means the two sexes look different. A mature bull is often close to twice as heavy as a cow. He has a taller hump, a broader head, thicker horns and a much longer mane, beard and leg hair, which make him look even bigger than he is.

Bulls keep growing for longer than cows. Females stop growing earlier, while males keep gaining weight for several more years, and the biggest bulls are usually older animals. The size difference matters in the breeding season, or rut, when bulls push and butt heads with rivals. Older, heavier bulls win most fights and father most calves.

Why does a bison look so huge?

Part of the bison’s impressive look comes from its shape. The shoulder hump is made of strong muscle anchored to tall spines on the vertebrae above the shoulders. These muscles hold up and swing the enormous head, which bison use like a snowplow to sweep snow off grass in winter.

The long, dense hair on the head, neck and forelegs adds to the effect, especially in winter. In contrast, the hindquarters are relatively slim and short-haired. Seen from the side, a bison is front-heavy, with its highest point above the front legs and its back sloping down toward the tail.

How big is a baby bison?

Calves are born in spring, mostly from mid-April to May, after a pregnancy of about 285 days. A newborn calf weighs about 15–25 kg (33–55 lb), roughly the weight of a medium-sized dog. It has a reddish tan coat and no hump yet; the hump and darker brown coat begin to appear after a couple of months.

Calves grow quickly and nurse for seven to eight months. Young cows can have their first calf at two or three years old, before they have reached full adult size.

Plains bison vs wood bison size

There are two forms of American bison. The plains bison lives in the Great Plains and Rocky Mountain parks such as Yellowstone. The wood bison, found in northern Canada and Alaska, is the larger of the two. Its hump is taller and more square, and its legs are longer.

Large wood bison bulls can reach about 2 m (6.6 ft) at the shoulder, and the heaviest recorded have weighed more than 1,000 kg (2,200 lb), up to about 1,180 kg (2,600 lb). At Elk Island National Park in Alberta, which has herds of both forms, about three-quarters of all bison heavier than 1,000 kg (2,200 lb) were wood bison. Bigger bodies help wood bison store fat and keep warm through long, very cold northern winters.

Record bison and the heaviest land animal in North America

The heaviest reliably weighed wild plains bison bull was about 1,270 kg (2,800 lb), and there are older, unconfirmed estimates of heavier bulls. Ranched bison fed for size have reached even higher weights, but those are not typical of wild animals.

This makes the bison the heaviest land animal in North America, ahead of the moose, which is taller but usually lighter, and of the largest brown bears. Worldwide, only a few wild relatives of cattle, such as the gaur of South and Southeast Asia and the wild water buffalo, match or exceed it. For comparison with other giants, see our list of the largest animals in the world.

How big is a bison compared with a person?

A big bull’s back is about as high as an adult man’s head, and his body is longer than a large sofa. He can weigh as much as a small car. Despite that bulk, bison can run at about 55 km/h (35 mph) and jump about 1.5 m (5 ft), which is why parks ask visitors to stay well away. Read more in are bison dangerous?