I'm hopeless at knowing the right food size for Karma. I'm feeding med. f/t hoppers right now, they seem to be a quite a mouthful for him but he seems hungry (in stalking/hunting mode) within 4-5 days after eating somtimes. He is about 20" and I still don't have a scale to weigh him with yet.
Here are a couple pics of him eating a week and a half ago:

The mouse doesn't seem as big in the pics as they seem in real life.
Here are acouple more so you can get a better idea of his size and girth: