How much caffeine is in a cup of coffee?

Where does the usual figure come from?

USDA's record for brewed coffee gives 40 mg of caffeine per 100 g, from eight samples that ran from 30 to 44, and its cup is 8 fl oz weighing 237 g. Multiplied out, that is about 95 mg a cup, and 71 to 104 mg across the samples. The multiplication is ours: the record we read gives the figure per 100 g, not per cup. 1151

It is a good number for what it measures: 8 samples of plain brewed coffee, analyzed in a lab and filed in a government database, poured into a cup most people would call small. Quoted without its source or its cup size, it reads like a promise about your mug. It was never that.

A 2014 study measured 104 espresso coffees bought in coffee shops in Scotland, Italy and Spain, with a few cappuccinos and instant coffees, and found 48 to 317 mg of caffeine per serving. It concluded that the term “one cup of coffee” is not a reproducible measurement. This is read from the abstract only. 54

“I’ve only had two cups” is a statement about crockery

How much caffeine is in a 12, 16 or 20 oz coffee?

Nobody orders eight ounces. So here is the same question at the sizes people drink, three ways: USDA’s coffee scaled up at about 11.8 mg per fl oz, FDA’s typical range, and what Starbucks states for its brewed coffee.

Read across any row. At every size, the Starbucks cup holds more than one and a half times what the USDA cup does, and its smallest size already clears the whole of USDA’s range for a cup. Per hundred millilitres, USDA’s coffee is about 40 mg per 100 g, since coffee weighs about what water does. Iced coffee and cold brew get their own comparison in cold brew vs iced coffee.

Venti is Italian for “I’ll sleep on Thursday”

Why does the same coffee from the same shop change?

In a 2003 lab study of specialty coffees, the same coffee bought from the same outlet on six consecutive days held 259 to 564 mg of caffeine per dose. Across the caffeinated coffees it tested, the abstract gives 58 to 259 mg per dose, and a mean of 188 mg (standard deviation 36) for brewed specialty coffee in a 16 oz cup. This is read from the abstract only, which does not name the outlet or the coffee, or give the serving size of the six-day samples. 53

Same order, same counter, six days running, and the strongest cup held more than twice the weakest. I have only the abstract, so I cannot tell you which shop or how big the cup was, and I will not guess. The point survives without it: a menu figure describes cups like these, not the one in your hand.

How much caffeine is in instant, espresso, decaf and pods?

Two things in that table surprise people. A shot of espresso is stronger by the sip and weaker by the serving: there is less in one shot than in a small cup of brewed coffee. And milk adds volume, not caffeine, which is why a tall Starbucks latte states the same figure as its single espresso and less than half of its smallest brewed coffee.

Dunkin’ and McDonald’s are missing on purpose. The copy of Dunkin’s nutrition guide we could read has no caffeine column, and we could not open McDonald’s United States menu at all, so we print no figure for either. Decaf is in the table because it is not zero, whatever the process: Swiss Water decaf included.

What changes the caffeine in a cup?

Four things. The order is our reading, from single studies that were not designed to be compared:

• How much coffee goes in. Caffeine comes out of the grounds, so more grounds per cup is more caffeine. One lab brewing strong, at one part coffee to ten of water, measured the equivalent of 199–251 mg per 8 fl oz from a French press. That is one coffee in one lab, set beside USDA’s figure from another, so treat the gap as a direction.
• The species. Green arabica beans run 0.9–1.5% caffeine by dry weight and robusta 1.2–2.4%, in a review that compiled other people’s measurements. By that pair of ranges the two overlap, so robusta is not reliably double. The same review also prints a narrower pair, 0.9–1.2% and 1.6–2.4%, that does not overlap. Nespresso puts its strongest espresso capsules down to robusta.
• The brew. In that strong recipe, a day-long cold brew came out at 234–291 mg per 8 fl oz, a little above the hot version of the same coffee, a gap the study found clear only for the coarse grinds.
• The roast, last. Across five roast levels and three brew times, one study found 134–165 mg per 8 oz cup for one coffee and 145–165 mg for another. Lighter roasts came out slightly higher in its long brews; measured another way, darker ones did.

Dark roast isn’t stronger. It’s just louder

How many cups of coffee is the daily limit?

The adult daily line of 400 mg/day, divided by the USDA cup, is about four cups. FDA does its own arithmetic on the same page as the limit and gets about two to three cups of 12 fl oz. By Starbucks’ stated range, one Venti brewed coffee can reach it alone. The single dose and the day, side by side, are in when a dose counts as a lot, and whether all those cups dry you out is in does coffee dehydrate you.

Coffee is rarely the whole day. The other usual suspects have their own pages: a Monster, a Coke Zero, matcha and chai, and what happens when you stop is under caffeine withdrawal.

400 mg a day is a guideline the way a speed limit is

The total is half the question. The other half is when, because caffeine leaves slowly: the half-life averages 4 hours, so a late-morning cup is still partly there at night. That average is the source’s; the instrument’s default is five hours, and you can drag it. The sums behind our chart are on the method page.