The family Ursidae encompasses eight distinct species whose masses vary more widely than any other land carnivore group. Defining an adult bear means the animal has reached full physical size and sexual maturity, typically between four and seven years of age depending on the species. The difference in size between the smallest and largest adult bears spans over 1,500 pounds, making a single average figure meaningless. To understand the scope of bear size, it is necessary to examine the specific weight ranges of the species across the globe.
Weights of North American Species
North America is home to some of the world’s largest bears, showcasing a dramatic size hierarchy. The Polar Bear (Ursus maritimus) is the largest bear species globally. Adult males generally weigh between 350 and 800 kilograms (770 to 1,760 pounds). Females are substantially smaller, typically ranging from 150 to 350 kilograms (330 to 770 pounds), a pronounced size difference known as sexual dimorphism.
Brown Bears (Ursus arctos), which include all Grizzly Bears, exhibit the greatest weight variability based on food sources. Coastal populations in Alaska have access to abundant seasonal salmon, allowing adult males to frequently weigh between 360 and 540 kilograms (800 to 1,200 pounds). The largest subspecies, the Kodiak bear, can achieve weights comparable to the largest polar bears.
Inland populations, commonly known as Grizzly Bears, inhabit mountain ranges and interior forests where food resources are less concentrated, resulting in smaller average sizes. Adult male Grizzlies typically weigh between 180 and 450 kilograms (400 to 1,000 pounds), while females are generally between 135 and 320 kilograms (300 to 700 pounds). The American Black Bear (Ursus americanus) is the smallest North American species. Adult males typically weigh 57 to 250 kilograms (125 to 550 pounds) and females range from 41 to 170 kilograms (90 to 375 pounds).
Weights of Eurasian Species
The Eurasian landmass features substantial bear species, though the largest generally do not reach the extremes of the North American giants. The Eurasian Brown Bear (Ursus arctos arctos) is closely related to its North American cousins but tends to be slightly smaller than the massive coastal forms. Adult males typically weigh between 250 and 355 kilograms (550 to 780 pounds), with females ranging from 100 to 250 kilograms (220 to 550 pounds). Subspecies in the Russian Far East can rival the size of the larger North American inland Grizzlies.
The Asiatic Black Bear (Ursus thibetanus), also known as the Moon Bear, is a medium-sized species found throughout Southern and Eastern Asia. This arboreal species has a lighter build compared to the brown bears. Adult males generally weigh between 60 and 200 kilograms (130 to 440 pounds), while females are typically 40 to 140 kilograms (88 to 310 pounds).
Weights of Smaller and Tropical Species
Bears adapted to tropical and subtropical environments represent the lower extreme of the weight spectrum, as hibernation is not necessary. The smallest bear in the world is the Sun Bear (Helarctos malayanus), found in Southeast Asia. Adult males weigh 40 to 70 kilograms (88 to 155 pounds), with females ranging from 25 to 50 kilograms (55 to 110 pounds). Their small size is an adaptation for their largely arboreal lifestyle.
The Sloth Bear (Melursus ursinus), native to the Indian subcontinent, has a diet focused heavily on termites and ants. Adult males typically weigh between 80 and 145 kilograms (176 to 320 pounds), while females are generally 55 to 105 kilograms (121 to 231 pounds).
The Spectacled Bear (Tremarctos ornatus) is the only bear species native to South America, found in the Andes mountains. This medium-sized species demonstrates considerable sexual dimorphism in mass. Adult males typically weigh 100 to 200 kilograms (220 to 440 pounds), while females range from 35 to 82 kilograms (77 to 181 pounds).
Factors Influencing Adult Bear Mass
The extensive weight ranges cited for all bear species fluctuate dramatically based on several environmental and biological factors. Sex is a major determinant of mass, as males in most species exhibit pronounced sexual dimorphism, meaning they are heavier than females. Male bears can be 30% to over 100% heavier than females, which aids them in competing for mates and defending territory.
Seasonal changes also cause fluctuations in an adult bear’s weight due to a process called hyperphagia. In preparation for winter hibernation, bears in temperate and Arctic zones enter a period of excessive eating to store fat, often increasing their body mass by 30 to 40 percent in the fall. This stored fat is metabolized during the denning period, meaning a bear’s weight in the spring is the lowest it will be all year.
Geographic location and the resulting diet composition are the greatest drivers of local population weight averages. The size difference between coastal Brown Bears and inland Grizzlies is directly attributable to the annual availability of protein-rich salmon along the coast. Bears inhabiting areas with high-calorie, concentrated food sources, whether natural or human-related, consistently achieve greater adult mass than those in food-scarce environments.