Its really hard to say how many exactly it needs. It all depends on whether it is really active, and its overall appetite. I would suggest feeding him two or three crickets at a time and watching the cham hunt them down. If he finishes those, add two or three more. Rinse and repeat this until he stops eating the crickets. Voila! You now have his ball-park number of crickets that he can eat. Its a tedious time consuming method, but it works and you really only need to do it once a month to monitor changes. I have had young yemen chameleons eat in between 5-20 crickets daily, there is really no set magic number. Cricket size is another determining factor. Let it eat its fill, I have never heard of a glutton chameleon. Also, dont feed it too many meal-worms, they dont digest well from what I have heard.