A full-grown beaver is about 30 inches (76 cm) long—not counting the tail—and weighs 35 to 60 pounds (16 to 27 kg); unusually large beavers sometimes weigh 110 pounds (50 kg) or more. The animals have small, rounded heads, small ears that can be closed when swimming, and powerful jaws. The body is thick-set; its back is humped. The forelegs are short with handlike paws that can be used to handle sticks and logs. The hind legs are much larger and permit the beaver to sit erect. The webbed toes on the hind feet make the animal a powerful swimmer.

The beaver is the biggest rodent in North America. An adult beaver is 3 to 4 feet (91 to 120 centimeters) long from its head to the end of its tail. The animal weighs from 40 to 95 pounds (18 to 43 kilograms).

Thousands of years ago, beavers were even bigger than they are today. Some were nearly 8 feet (2.4 meters) long. Scientists are not sure why beavers have become so much smaller.

A beaver’s back feet are 6 to 7 inches (15 to 18 centimeters) long. Each foot has webbed toes with strong, split claws. The webbed feet work like flippers to make the beaver a strong swimmer.

A beaver’s fur is helpful in many ways. For example, it is so thick that it can protect the beaver from insect bites and pointy sticks.

Fur also helps a beaver in the water. A beaver can waterproof its fur by combing in its body oil with its claws. Once the fur is waterproof, it helps keep the beaver warm as it swims.

Fur keeps a beaver comfortable in cold weather, too. The fur traps body heat underneath. It acts like a blanket to keep the beaver warm, even in freezing weather.

Fur also helps a beaver stay safe. Its brown color lets the beaver blend in with trees and bushes. That way, beavers can hide from their enemies.

The beaver's teeth are used to cut down trees needed for food as well as for dams. There are two cutting teeth, or incisors, in each jaw. They are curved with chisellike cutting edges, capable of cutting through trees two feet (60 cm) thick. Although the tips are worn away by constant gnawing, the teeth remain approximately the same size because they continue to grow throughout the animal's lifetime.

A beaver, like all rodents, has four incisors. A beaver has two incisors in its upper jaw and two in its lower jaw. Beavers use their incisors to gnaw.

The front of each incisor has a very hard orange coating. The back of each incisor is much softer. It wears down faster than the front. As a beaver gnaws, this difference in hardness allows each incisor to form a sharp edge, like the edge of a chisel.

Incisors are not a beaver’s only teeth. A beaver also has 16 back teeth that are used for chewing.

In between a beaver’s front and back teeth is a long gap. In this gap are flaps of skin that actually separate the front and back of the animal’s mouth. This helps a beaver gnaw wood without swallowing splinters. A beaver can also gnaw in a pond without swallowing water. If this rodent wants to eat or drink, it just opens its skin flaps.

The beaver's broad, flat, scaly tail is 8 to 12 inches (20 to 30 cm) long. Shaped like a canoe paddle, it is used as a rudder in swimming. The first beaver to see an approaching enemy sounds an alarm by slapping the water with its tail.

A beaver’s tail looks somewhat like a boat paddle. It is about 12 inches (30 centimeters) long and 6 to 7 inches (15 to 18 centimeters) wide. The tail has scaly skin and almost no hair.

A beaver’s tail is quite useful. In the water, it helps the beaver steer while swimming. On land, the tail supports the beaver when it stands up to eat or cut down trees.

A beaver’s tail also comes in handy as a storage space. It stores body fat that supplies the beaver with energy when food is hard to find. In addition, the tail stores two body oils. The beaver uses one oil, castoreum (kas TAWR ee uhm), to mark its territory. It uses the other oil to waterproof its fur.

The tail serves as a defense weapon, too. If a beaver senses danger, it slaps its tail hard on the water. The loud noise warns other beavers in the area to take cover.