UKC Pitbull Standards

In 1936 the United Kennel Club, which was put together by dog fighters, had standard pitbull weights listed as follows:
Females preferred from 30 to 50 pounds.
Males from 35 to 60.

Today's UKC standard states: The APBT must be both powerful and agile. Actual weight and height are less important than the correct proportion of weight to 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. Dogs over these weights are not to be penalized unless they are disproportionately massive or rangy.

Read more about UKC standars for American Pitbull Terriers at http://www.ukcdogs.com/RegUKCBreeds.htm