normal weight gain
 

my corn snake is 66g and around 9 months old which i thought was quite small so i moved him up from 3-5g mice to 10-15g mice every 6 days (the shop didnt have an inbetween size) he has gained 8 grams in the last week and i just wanted to ask if thats a normal amount of weight to gain or if i should decrease the size/frequency of the mice?

66 grams is a great weight for his age. Your bigger mice are a tad on the large side, so I would definitely feed him the ones that are closer to 10 grams first. And I would only feed once a week.

My one year old is almost 90 grams and I have him on 9g fuzzies at the moment. Like hypnoctopus said, try to feed him mice closer to 10g and feed a little less frequently. As long as you don't have any issues with regurge it should be fine. And I've found that young corn snakes are very efficient with their food. A good proportion of the weight of the food is converted to weight of the snake. Sounds like your baby is off to a good start.