I use 6qt bin for up to about 500 grams, 12 qt bins to around 900 grams, 28 qt bins until about 1800-2000 grams, and 41 qt bins for large females over 2000 grams. I will also move them down a tub size if they go off feed in the winter as well. I feel these are the most common animal size to tub size so its a good starting point, but you just need to see how yours respond to being in larger or smaller bins.