How Big Are Polar Bears? Polar Bear Size, Weight and Records

Polar bear size at a glance

Polar bears show one of the strongest size differences between the sexes of any mammal. Males are not only heavier but also longer, with bigger heads and thicker necks. The table gives typical ranges for healthy adult polar bears in the wild.

Some references give an even wider male range, up to about 800 kg (1,760 lb), because weights change so much through the year. The tail is tiny for such a big animal, which helps reduce heat loss.

Why polar bears are so big

Large size is an advantage in the cold. A big body has less surface area for its volume than a small one, so it loses heat more slowly. This pattern, known as Bergmann’s rule, is seen in many mammals that live in cold places, and the polar bear is an extreme example.

Size also suits the polar bear’s way of hunting. Its main prey, the ringed seal, weighs around 50–70 kg (110–155 lb), and big males regularly tackle bearded seals that can weigh over 300 kg (660 lb). A heavy bear can pull a seal out of a breathing hole and hold on to it. Finally, the bear’s main food is blubber, an energy-rich fat, which allows it to build and keep a huge body. For more on its prey, see what do polar bears eat?

How much does a polar bear’s weight change in a year?

A polar bear’s weight is not fixed. Bears can increase their body mass by up to about 50% when hunting is good, mainly in spring and early summer when young seals are plentiful on the ice. They then lose much of that weight while fasting on land in summer and autumn or while denning.

Pregnant females show the biggest swings. Before entering a maternity den in autumn, a well-fed female may weigh up to about 500 kg (1,100 lb). She then goes without food for up to about eight months while giving birth and nursing her cubs, and she can lose around 40% of her body weight before she returns to the sea ice to hunt.

Because of these changes, a single figure for “the” weight of a polar bear is misleading. A male weighed in late autumn after a long summer fast can be far lighter than the same animal in June.

How big are polar bear cubs?

Polar bear cubs are surprisingly tiny at birth. They are born between November and January in a snow den, usually as twins, and each weighs only about 600 g (1.3 lb), less than a guinea pig. Newborns are blind, toothless and covered in short, fine fur.

Their mother’s milk is around 30% fat, and the cubs grow quickly. By the time the family leaves the den in March or April, each cub weighs about 10–15 kg (22–33 lb). Young bears stay with their mother for about two and a half years. Females reach full adult size at about four or five years, while males keep growing until they are about eight to ten.

The largest polar bear on record

The heaviest polar bear on record is a male reportedly weighing about 1,002 kg (2,209 lb), which was killed at Kotzebue Sound in northwestern Alaska in 1960. This figure is widely quoted, but it has never been independently verified, so it should be treated as an exceptional and uncertain record rather than a normal size.

Reliable weights of wild bears measured on scales during research are far lower. Even very large males caught and weighed by scientists rarely exceed about 700 kg (1,540 lb). Claims of polar bears “over 1,000 kg” in books and online are usually repetitions of the 1960 record or estimates made by eye, which tend to exaggerate.

Polar bear vs Kodiak bear: which is the largest bear?

On average, the polar bear is the largest living bear. However, the biggest brown bears, especially Kodiak bears from Alaska’s Kodiak Archipelago and coastal bears of the Alaska Peninsula, overlap with polar bears in size. Large Kodiak males commonly weigh around 480–635 kg (1,050–1,400 lb) in autumn, so the very largest individuals of the two species are similar.

Polar bears are built differently from brown bears: longer and more streamlined, with a longer neck and a narrower head, and without the brown bear’s muscular shoulder hump. For a full side-by-side comparison, read polar bear vs grizzly bear, and for brown bear figures see how big do grizzly bears get?

Are polar bears getting smaller?

In some regions, yes. Long-term studies in Western Hudson Bay in Canada have found that bears there are, on average, lighter and in poorer condition than in the 1980s. The main cause is a shorter sea ice season: when the ice breaks up earlier in summer and freezes later in autumn, the bears have less time to hunt seals and must live longer on stored fat.

Smaller, thinner females produce fewer and lighter cubs, and fewer of those cubs survive. Body condition is therefore one of the main signs scientists use to track how polar bears are coping with a warming Arctic. Not every population shows the same trend, and some in areas with more stable ice remain in good condition.