I don't drink coffee; I drink black tea, which has less caffeine per cup than coffee - but I drink a lot of it.
And I mean a lot.
One of my favourite tea mugs fits nearly a liter of tea in one go. Yes, a liter-sized mug. I can go through several of those a day. On days when I do a lot of work (and therefore need to focus; I focus better with a tea mug in hand), I measure my tea-intake in pots, not cups.
But like I said, there's less caffeine per tea cup than there is per coffee cup, so I probably don't get as much caffeine as people who drink a lot of coffee.