The average length is 35 to 52 inches measured from the head to the tip of the tail. Adult beavers weigh 40 to 70 pounds (18 to 32 kg) . Records of 96 pounds (44 kg) for a Missouri beaver and the largest castor canadensis was 110 pounds (50 kg) from Wisconsin. After late summer beavers start putting on weight. This makes it easier to deal with the freezing winter temperatures relying o extra body fat for insulation. Kits weigh 9 to 15 pounds (4 to 7 kg), by the age one they are 21 pounds (10 kg) and by age 2 they are 30 pounds (15 kg). From the time they are born the beaver uniquely never stops gnawing.
The beaver tail has many uses. On land they use it when tree felling to support themselves, to balance when carrying mud walking on hind legs. In the water beavers can turn their tails in four directions to act like a rudder while swimming. The surface is leathery with a fish like look, coarse hairs cover the tail where it joins the body. Tails measure 6 to 12 inches (15 to 30 cm) long and 4 to 5 inches (10 to 13 cm) wide and about 3/4 inch (15 mm) thick. Beavers have a stout body size with legs that have separate lower leg bone, unlike rats and mice that have fused leg bones. The feet have evolved to carry out different jobs. The front feet are short and look like small web-less hands with sharp pointed claws that are excellent for moving branches and digging into mud banks or tearing up vegetation for feeding or construction. Beavers intelligence is above all rodents other than the Norwegian rat. The hearing sense is highly developed and can easily classify dangerous to friendly sounds. The ears of the beaver are small and when swimming valvular flaps close tightly, stopping water entering the auditory canal. Beaver lips are large and close behind the teeth. They are covered with fur. This allows beavers to carry branches while swimming and cut material under water. Beaver eyes are not really good. They can see but they rely more on sound and smell.