How do you distinguish a black bear from a grizzly bear

Size is a poor identifier as both bears vary greatly in size. Male grizzlies average 225 kg (500 lbs), with females averaging around 160 kg (350 lbs). Large bears may tip the scales at 360 kg (800 lbs). 

Black bears average 50-140 kg (110-300 lbs). Large male bears can top 180 kg (400 lbs) and may be larger than female grizzlies, so size is not an accurate indicator. 

Grizzly bears stand around 1 m (3.28 ft) at the shoulder and may stand 2 m (6.5 ft).

Black bears are slightly smaller at the shoulder, between 0.75 to .9 m (2.5 to 3 ft). When standing erect, they rise around 1.5 m (5 ft). 

In profile, the grizzly bear has a distinct shoulder hump. This is due to large muscles necessary for digging roots, tubers and ground squirrels.

Black bears lack the shoulder hump of the grizzly.

Grizzly bears have a dished-in profile, with a clear depression between the eyes and the end of the nose. Grizzlies also have short rounded ears.

Black bears have a "Roman" profile, with a straight line running between the forehead and the tip of the nose. The ears of black bears are larger and more distinctly pointed. 

The claws of a grizzly have a formidable reputation. Very long, between 5-10 cm (2-4 in), they are often clearly visible in the tracks. They may also be visible from a distance.

Black bear claws are much shorter than those of grizzly bears, usually around 4 cm (1.5 in). They are less visible from a distance and play a minor role in track records. 

Grizzly tracks have a minimal arc in the toes. Simply stated, if you line up a straight edge with the base of the large toe, and then with the front of the foot pad, the other end should run between the middle and base of the small toe. Often the long claws are clearly visible in the track.
The toe imprints of grizzly bears are close together, usually touching each other. 

Black bear tracks have a large toe arc. If you line up a straight edge with the base of the large toe, and then with the front of the foot pad, the other end should run between the middle and tip of the small toe. The shorter claws of the black bear often do not leave a visible impression in the ground.
The toe imprints of black bears are farther apart, often with a definite space between the toes.