Um looks like you answered your own question haha? It depends on what kind of stuff it is, for example 1 liter of water is 1 kg but 1 liter of hay is not 1 kg. But seems like you figured it out. I don't know the brand either. Do they sell smaller packs? It makes it easier to try out, if you find out your buns refuse to eat it you will be swimming in useless hay.