Here is this from the UKC standard which is closer to original. Note the limits on weight.

The American Pit Bull Terrier must be both powerful and agile; overall balance and the correct proportion of weight to height, therefore, is far more important than the dog’s actual weight and/or height.
Desirable weight for a mature male in good condition is between 35 and 60 pounds. Desirable weight for a mature female in good condition is between 30 and 50 pounds.
As a general and approximate guideline only, the desirable height range for mature males is from 18 to 21 inches at the withers; for mature females it is from 17 to 20 inches at the withers.
It is important to note that dogs over or under these weight and height ranges are not to be penalized unless they are disproportionately massive or rangy.
Very Serious Fault: Excessively large or overly massive dogs and dogs with a height and/or weight so far from what is desired as to compromise health, structure, movement and physical ability.