How many bingo cards can one person play at once?
Most people can comfortably hand-mark about four to six bingo cards at once, and in most games there is no rule stopping you from buying more than that.
The limit is time, not rules. A caller who leaves five seconds between numbers gives you five seconds to check every card in front of you. Finding one number on a 5×5 card takes roughly a second once you know the layout, so four to six cards fit inside that gap with a little margin; twelve do not, and you will start missing marks.
The traditional 90-ball purchase is a strip of six tickets, and that number is not an accident: the six tickets between them hold every number from 1 to 90 exactly once, so every single call marks exactly one square. Six is about as much as one pair of hands can keep up with.
Past six cards, players either ask the caller to slow down or hand the tracking to a phone, which can follow dozens of cards at the same call speed without missing one.