I usually feed something larger than the thickest part of the body but since I only have small mice at the moment I feed two of those every seven days. (Mine's around 160 grams). So I guess that would be around 10-15%. I've never really been worried about feeding something too big though because from what I've seen and heard from breeders carpets are one snake that can take really big meals with no negative consequences (my breeder said he started mine off with large fuzzy or hopper mice right off the bat).