The length of the rear paw is not a great indicator of size.As a rough guide take the width of the front paw ,add one and this will be the approximate length in feet of the bear.Of course this is only approximate because bears feet vary in size in relation to their body size like humans.I have seen many bear tracks both black and grizzly and the numbers provided by the outdoor life article seem inaccurate and basically meaningless to me as both black bears and grizzlies vary so much in size.Many black bears are in fact larger than many grizzlies.