If I were wearing an N95 just for the weekly grocery store run, I’d probably be fine with alternating two carefully handled masks for many months as long as the elastic works and there’s no soiling. That’s not a lot of use! But if I were wearing one all day, every workday, I’d consider having one for each day and replacing them maybe every month. So that’s about five per month. Could one be really careful and make that two months? Probably.