The sperm whale is the largest of the toothed whales, with males reaching a maximum length of aboput 50 to 65 feet (15 to 20 meters). Females are smaller, reaching a maximum length of about 36 to 55 feet (11 to 17 meters). The body weight differences between males (averaging 45 tons) and females (averaging 20 tons) is the largest (between the sexes) of any whale.

The head of the sperm whale measures between one-quarter to one third of the body length.

The large head contains a huge cavity called the spermaceti organ.

The single slitlike blowhole is located near the front of the head, on the left side, producing an angled, "bushy" blow of up to about 15 feet (5 m) in height.

The color of sperm whales is variable, from brownish grey to black. Whitish areas occur around the lips, and individually at the front of the head and around the naval.

The skin of the sperm whale is extremely thick, reaching nearly 15 inches on the back and sides. Wrinkles run horizontally over the rear two-thrids of the body.

The tail, raised straight up into the air when diving, has two broad, triangular flukes with a distinctive notch in the middle, and may measure over 13 feet (4m.) from tip to tip.