No. Espresso has the highest concentration of caffeine, packing about 70 milligrams into a one-ounce shot, but is consumed in smaller quantities. By comparison, a typical 12-ounce serving of drip coffee has 200 milligrams of caffeine, more than instant’s 140. And, yes, brewed decaf has caffeine, too — 8 milligrams — which can add up.

When buying coffee, you never really know what you’re going to get. At one Florida coffee house, over a six-day period, the same 16-ounce breakfast blend fluctuated from 259 milligrams all the way up to 564 — which goes beyond federal recommendations.

But for some of us, knowing how much caffeine is in our coffee can be especially important. You’ve probably noticed it before. How a friend can pound quadruple espresso shots at 10 p.m. and sleep afterward, while you can’t have any past noon, or you’ll be watching “Seinfeld” reruns until dawn. Some of us have a polymorphism, a genetic variant that slows our metabolism for caffeine. It’s these individuals that Dr. Grosso recommends limit their refills. “They take a coffee, and then they have the second and the third, and they still have the caffeine of the first,” he said.