There's some confusion over the term "pit bull" as it's often used to refer to multiple breeds. American bulldogs are occasionally called pit bulls, but they're distinct from the pit bull type. American staffordshire terriers, American pit bull terriers and Staffordshire bull terriers all come under the pit bull umbrella.
A Brief History
Although the name pit bull refers to more than one breed, they all have the same origins. In fact, some breeders consider the American pit bull and the American Staffordshire terrier the same breed. The United Kennel Club registers American pit bulls whereas the American Kennel Club registers American Staffordshire terriers. However, an Am Staff registered with the AKC also can be registered as an American pit bull with the UKC and vice versa. Both these dogs and the Staffordshire bull terrier come from British lines, where they were developed by breeding various terriers to an archaic breed of bulldog. American bulldogs, on the other hand, come from mastiff lines and were a result of breeding bull mastiffs and other varieties of mastiff.
Size Matters
One of the most obvious differences between pit bulls and American bulldogs is their size. According to the UKC, there's no exact height range for American pit bulls, but there should be a height to weight balance. Therefore, since their weight shouldn't exceed 60 pounds, they should measure no more than 20 inches at the shoulder. The AKC states American Staffordshire terriers should measure between 17 and 19 inches at the shoulder and Staffordshire bull terriers between 14 and 16 inches. American bulldogs are much larger -- they should weigh between 60 and 125 pounds and measure between 20 and 27 inches at the shoulder.
Snouting for Dogs
You can differentiate between pit bulls and American bulldogs by looking at their snouts and heads. All pit bull types should have a snout of an equal -- or slightly longer -- length to that of their skulls. American bulldogs, however, should have a skull that's longer than their snout. If you look at their head as a whole, their skull should make up between 55 and 80 percent of the length, with their snout accounting for the remainder.
Wrinkle Me This
Due to the lineage of these dogs, you can tell American bulldogs and pit bulls apart by looking at the skin on their faces. American bulldogs' mastiff ancestry has given them slightly loose and wrinkled skin on their heads and around their mouths. By contrast, pit bulls -- who have terrier lineage -- have taught facial skin and very rarely have any wrinkles on their heads.