Of course this also depends on where in the world you are drinking coffee: in the US, the coffee is not as strong as in other parts of the world, so people in the US drink in larger quantities (8 oz cups) than others (about 1.7 oz), but the caffeine amount is also different.
Maybe this could give you an idea?
http://www.talkaboutcoffee.com/how_much_is_too_much2.html Or maybe this?
http://en.wikipedia.org/wiki/Caffeine (see second table on the right, with caffeine contents in food and drugs)
malu
