Grizzly Bears - North Cascades National Park (U.S. National Park Service) Grizzly bears are mammals. An adult grizzly bear can measure 3-4 feet (+/-1 meter) high at the shoulder and 8 feet (2.4 meters) tall standing upright. The foods they eat determine how big each individual will be. In an ecosystem similar to the North Cascades, where bugs and berries are predominant foods, adults weigh between 250 and 600 pounds (113-272 kilograms).