How heavy is a grizzly bear?

The US Fish and Wildlife Service gives adult male grizzlies in the lower 48 states 400 to 600 lb (about 180 to 270 kg) and adult females 250 to 350 lb (about 110 to 160 kg). So a 270 kg (595 lb) male is a large, well-fed adult rather than an average one.

Yellowstone has some of the best measured grizzlies anywhere, because biologists have been catching and weighing them since the 1970s. The park lists an average adult male at 187 kg (413 lb) and an average adult female at 122 kg (269 lb). The heaviest male ever recorded there weighed 324 kg (715 lb) in 1977, and the heaviest female 198 kg (436 lb).

A grizzly is at its leanest around the end of June, when Yellowstone bears usually carry 15 to 20% body fat. Through late summer and autumn they eat almost constantly to fatten up for winter, and by October females typically reach 28 to 30% body fat and males about 32%.

One Yellowstone male, Grizzly 566, shows how far that can go. Caught at 3 years old in 2007 he weighed 232 lb (105 kg). In October 2023, aged 19, he weighed 712 lb (323 kg) with 41% body fat, the second-heaviest grizzly ever documented in the Greater Yellowstone Ecosystem.

All that fat is what gets a bear through winter. Yellowstone grizzlies lose 15 to 30% of their body weight while hibernating, so a bear that goes into its den in autumn comes out in spring noticeably lighter.

Grizzlies and brown bears are the same species, Ursus arctos. In Alaska, bears living along the coast are usually called brown bears and those in the interior and north are called grizzlies. Coastal bears with steady access to salmon grow much bigger than inland grizzlies that live on roots, seeds, insects and the occasional elk or bison.

In Katmai National Park, adult males weigh 600 to 900 lb (272 to 408 kg) in midsummer and the biggest pass 1,000 lb (454 kg) by late autumn. Adult females average about a third less. The Alaska Department of Fish and Game puts the largest brown bears at up to 1,500 lb (680 kg).

Katmai’s Fat Bear Week, held each year in late September, celebrates that autumn bulk. The bears are not actually weighed; the public votes from before and after photos. The 2025 winner, a large male known as Chunk, was estimated at about 1,200 lb (544 kg).

The hump between a grizzly’s shoulders is muscle, not a store of fat. Yellowstone National Park describes it as a large muscle mass above the shoulders, and bear identification guides explain that these well-developed shoulder muscles power digging and turning over rocks. Grizzlies dig a lot, for roots, bulbs and burrowing rodents, which is also why their front claws are long and only slightly curved.

The hump is a useful way to tell a grizzly from a black bear, but it depends on posture and terrain. A black bear with its head down can show prominent shoulder blades that look a lot like a hump.