The two birds are difficult to tell apart, but the primary difference between a raven and crow is that the raven is larger and heavier. The raven also has a thicker bill and a wedge-shaped tail, while a crow's tail is rounded and straight.
The common raven is about 21 inches long and is normally found in the forests of northern Canada and the western United States. When it flies, it flaps its wings less often and soars more than a crow and can be mistaken for a hawk. The common raven also eats more carrion than a crow.
The common crow is about 17 inches long and is abundant across most of North America, save for the desert of the Southwest. It also makes a distinctive "caw" sound, while the raven's call is more of a croak.