There are no federal standards for exactly how much caffeine is allowed in coffee that is labeled as ‘decaffeinated’. A general rule of thumb, though, is that an eight ounce cup of decaf coffee (quite small, actually) would contain around five milligrams of caffeine. For comparison, a cup of regular coffee would have around 60 to 120 milligrams of caffeine. The results of an independent test of retail coffee showed some with twice the normal levels of caffeine, with the worst being eleven milligrams of caffeine in the decaf coffee from Dunkin Donuts. Now, the truth is, we’re talking about pretty small differences, but it is interesting and not entirely unexpected, as caffeine extraction is a process which is potential subject to all sorts of variables (along those lines, the coffee provider for Chick-Fil-A has a spec of 1.5 to 8 milligrams of caffeine in their decaf coffee). For more about this study, follow this link.