The general guideline is one litter box per cat, plus an extra. So for 2 cats, 3 litter boxes are ideal. This allows them each to have their own space and prevents issues like one cat blocking the other from using the litter box. However, some cats are comfortable sharing 2 boxes as long as they are scooped frequently. Monitor your cats' litter box habits and add an extra box if needed. More boxes can also spread out waste to extend time between ScoopFree tray changes.