Two came with Roomba and one I used for many months without reading the instructions first then replaced with the second and wanted to make sure I had enough spares to change every 2 months as stated i bought a pack. But let's get to how this filter works: It retains fine dust well and can be easily shaken off after a light tap on the wall of the garbage can. I run Roomba at least once a week in my 1,600-foot house and several times a week in certain rooms like the dining room, kitchen, and living room.