we did a breeding project at tafe with mice, we had to breed two generations and weigh them weekly etc, at birth (pinkies) the mice weighed 1-2g each, at 2 weeks (fuzzies) they weighed 3-4g each and at 3 weeks (weaners) they weighed 5-7g each so theres really not much difference between the weaners and fuzzies, at 6 weeks they weighed 16-18g each and as adults they weigh about 30g, my stimson is 10 months old and i feed her small weaners, it also depends on the breed of mice i guess, the ones on that website are balb/c, we bred c57bl.dba2 but they should be around the same weights, i also didnt know that rats were better food to provide, it thought theyd be nutritionally the same so itd be interesting to find out how they benefit =)