I don't weigh them at the store, but I do weigh them before I feed them. I try to get my BP's about 20g of food per 500g of weigh or so (maxed at 60g), and don't feed anything less than 15g to even my smallest (250g) BP. I also weigh them before I euthenize the ones I'm breeding, and if they're not at 20g they go back in the bin...