A polar bear's stomach can hold an estimated 15% to 20% of its body weight. A polar bear generally eats this much only when its energy demands are high. A bear can assimilate 84% of the protein and 97% of the fat it eats.

Polar bears need an average of 2 kg (4.4 lb.) of fat per day to obtain enough energy to survive.

A ringed seal weighing 55 kg (121 lb.) could provide up to eight days of energy for a polar bear. Hibernating polar bears do not eat.

More Info: seaworld.org