The one thing your not taking in to account when asking how everyone calculates their feeder needs, is that not every one is able to feed F/T..I can't none of my snakes take F/T so every week I have to have the right number of live feeder items of the right size for every one of my 70+ snakes. With so many being smalls, so many being chubs and so many being weaned. This means that at any given time I have to birth 100+ rats a week, so that the babys that get fed every 5 days will have food available and that I'll still have enough growing up to feed the rest in how ever many weeks.

To calculate your output is going to depend on you and how you breed how many and what size animals you feed off. If you've seen an average number of rats born a week-month-year I'd go with that number. Since no one but you knows the variables no on but you can arrive at that number.