The weight can very depending on what bloodlines,male or female ,and any possible abnormalities,such as being a runt or digestive problems and the diet being administered. I have had a red nose that weighed around 50 pounds at seven months but have also had one at seven months that only weighed around 30.
My 7 month old pit weighs about 55 lbs and he is currently getting 1 1/2 cups twice a day. If you are uncertain, read the dog food bag- it should tell you based on weight how much to be feeding your dog. Keep in mind that pitbulls should be muscular, but you should be able to feel their ribs when rubbing their side.
I have a 7 month old red nose and she weighs almost 70lbs. She isn't fat or to muscular either. I do believe there blood line makes a difference.
I have a 7month old family rednose pit he weighs about 60lbs he was the runt of the litter. So I think its all in the blood lines.