Typically, one 20-lb. bag of litter per cat will last one month. Our litter lasts longer than many other brands because our sun-dried clay is known for its superior ability to absorb liquids and clump quickly. This results in tighter clumps and less litter used. How long a bag of litter lasts also depends on how many cats you have, their size and waste habits, and what type of litter box they use. For example, a self-cleaning litter box like the Litter-Robot helps reduce litter usage by up to 50% as compared to scooping a traditional litter box.