Mmmmmmm! That's a right tricky one! A lot depends on the breed as some tend to be a bit bulkier than others. Boars are usually a bit bigger than sows. I'd worry if a piggy was suddenly putting on a lot of weight, or having trouble moving around, or breathing was laboured (or if they suddenly lost weight). I'd certainly worry if a piggy went over the 3.5 lb mark. There's a sticky at the top of this section with weights of some of our piggies - take a look, it's really interesting. 88)