Well, I can't weigh him right now anyways. He ate less than 4 hours ago and he does have a habit of regurgitating (hence feeding him in his tank). So what I'll do is tomorrow or the next day I will weigh him, and check to see what 10-15% of his weight is. If the percentage and the "girth" method match in size of prey, I'll stick to that size of prey. If the two methods don't match, I'll pick a prey size between the two. I am also going to put him on a closer schedule if the percentage method points to staying with mice (which I doubt) and check for signs of weight loss.