Here is a generic scale of aprox weight of prey
I would also look for a local breeder or supplier of feeders I just think they have better quality rodents for the most part than those offered in most CHAIN pet stores Plus they are usually a lot cheeper I pay about $1.25 for small rats and price goes down from there
MICE
Sm. Pink 1-2 grams
Lg. Pink 2-4 grams
Peach Fuzz 4-6 grams
Fuzzies 5-8 grams
Hoppers 8-12 grams
Sm. Mice 11-16 grams
Med. Mice 15-24 grams
Lg. Mice 24-28 grams
XLg. Mice 30 grams+
RATS
Rat Sm. Pink 3-8 grams
Rat Lg. Pink 5-12 grams
Rat Fuzzies 10-20 grams
Rat Pup 20-30 grams
Rat Wean 30-45 grams
Rat Sm. 40-80 grams
Rat Med. 80-150 grams
Rat Lg. 140-200 grams
Rat XLg. 190-250 grams