Bears (also called ursids, in reference to their family Ursidae) are, as a group, the largest extant terrestrial carnivores. Many carnivorous marine mammals are larger, but the focus here is on land-dwelling species.
The graph at top left shows the median and range of body sizes for species within each of the families of terrestrial carnivores. This provides a visual sense of just how much larger bears are compared to other carnivorans. The only exceptions to this rule are the two largest cats, or felids, represented by the outlying dots above the Felid bar. These represent the tiger and the lion.
Another way to reckon size is by dimensions of the skeleton, represented in the bottom left graph by the size of the jaw (i.e., mandible). Here, again, bears are the largest, but not by as much of a margin--although this is visually distorted by the fact that the y-axis to the left is of log-transformed values, which tends to compress things. Even so, the median size of jaws among the bone-crushing hyaenas is nearly as large as the jaws of bears.
The bottom line: Ursids are exceptionally large, especially when compared to other contemporary land-dwelling carnivores.
Given that fact, there are many consequences that flow from being large. Species tend to live longer, reproduce at a slower rate, and metabolize at a slower rate (at least per unit body mass). The following link takes you to a page that elaborates on all of this, including how bears conform to the expectations of large body mass--and also how they deviate.
A second link, which follows, takes you to a page that offers a few more details on how the body size of brown/grizzly bears varies in space, among populations, and between the sexes--as well as how size has varied in recent epochs.
A final link (below) takes you to a page that shows how bear size changes with age, emphasizing data from the Yellowstone grizzly bear population.