I am not sure if there is a standard, but I would hope there is. Follow this link http://www.bigcheeserodents.com/Pricing.html
It lists the weight of all sizes of mice and rats. They also offer cheap shipping and I have been happy with the product. I have them shipped by bus and have never had a problem.
i know the weights of my feeders. my hatchlings now get either a rat fuzzy or pup and they can weigh anywhere from 20-40 grams. i was asking about the weights of the OP's 3 year old adult animals that are supposedly eating the same sized rodents as my hatchlings.
