Hi, im on straw too and its awful. My horse is filthy and eats her bed and also kicks it back so has nothing to lie on. Been trying to persuade my mum to change to rubber mats and shavings or easibed for my horses sake and ours. Anyway you need 10 - 12 bags if you have no mats and 6 - 8 if you do. Ive been researching lol .