Short answerA standard 1 oz shot of espresso carries about 63 mg of caffeine. Starbucks pulls a larger shot at roughly 75 mg. The FDA describes 400 mg a day as not generally associated with negative effects in healthy adults — about six standard shots.
A standard 1 oz shot of espresso carries about 63 mg of caffeine, so a double is roughly 125 mg and six shots reach 378 mg — right at the FDA’s 400 mg daily ceiling. Starbucks pulls stronger shots at about 75 mg each.
| Shots | Standard espresso | Starbucks strength | Share of the 400 mg cap |
|---|---|---|---|
| 1 shot | 63 mg | 75 mg | 16% |
| 2 shots | 126 mg | 150 mg | 32% |
| 3 shots | 189 mg | 225 mg | 47% |
| 4 shots | 252 mg | 300 mg | 63% |
| 5 shots | 315 mg | 375 mg | 79% |
| 6 shots | 378 mg | 450 mg | 95% |
Every article in this section works from this table, which is why no two pages here will give you different answers to the same question.
Espresso is the most concentrated way to drink coffee and one of the weakest servings by total caffeine. Concentration and dose are different things. A shot is 1 oz of very strong liquid pulled from 7 to 9 g of grounds; a 12 oz mug of drip is a weaker liquid pulled from 15 to 20 g. More grounds and more water mean more caffeine in the cup, even though each mouthful is milder.
| Drink | Caffeine |
|---|---|
| Single espresso, 1 oz | 63 mg |
| Double espresso, 2 oz | 126 mg |
| Drip coffee, 12 oz | about 140 mg |
| Instant coffee, 8 oz | about 60 mg |
| Black tea, 8 oz | about 47 mg |
| Cola, 12 oz | about 34 mg |
| Energy drink, 8 oz | about 80 mg |
| Variable | Effect on a shot |
|---|---|
| Robusta in the blend | Up sharply — roughly twice the caffeine of arabica by weight |
| Double basket, 18 g dose | Roughly doubles it — what many bars serve as a "single" |
| Ristretto, short pull | Down 10 to 20 percent |
| Lungo, long pull | Up 10 to 20 percent |
| Dark roast | Slightly down by weight — roasting burns off a little caffeine |
| Decaf | Not zero: about 3 to 8 mg per shot |
The largest source of confusion is the word "shot" itself. In Italy a single is 7 g and 1 oz. In most speciality bars elsewhere the default basket is 18 g, so what you are handed as a single espresso is closer to two Italian shots.
Caffeine has a half-life of roughly five to six hours in a healthy adult, so half of what you drink at 4pm is still circulating at 10pm. That is the mechanism behind the common complaint that caffeine has no effect but sleep is poor anyway: tolerance builds against the alertness effect far faster than against the sleep disruption. Variation in the CYP1A2 enzyme means some people clear caffeine in half the time others take, which is why a shared cut-off time is useless advice and a personal one is worth finding.