Simply take a pair of scissors and cut the 3 active carbon filters down to the required size for your own covered litter box and place them inside. You should get about 912 replacement carbon filters to a pack for your covered litter box, depending on the size of the filter once cut down. Filters that contain active carbon come in handy in plenty of ways for cleaning up air and gas. The very large inner surface area of the active carbon absorbs nasty odours very effectively. Particularly organic compounds attach themselves to the branched pore structures of activated carbon and prevent them from being released into the surrounding air. And once the active carbon is saturated with toxic gases and unable to absorb any more odours, simply cut a new filter out the from replacement pack and place it in your cats covered litter box. Active carbon filters should be regularly replaced. Universal Active Carbon Filters at a glance: Universally applicable active carbon filters for all covered