The FDA’s 400 mg daily ceiling works out to about six single shots of espresso, or three doubles. Sensitivity varies widely, and anything after mid afternoon can cost you sleep.
Related conversions
The arithmetic rests on about 63 mg per single shot, or about 126 mg for a double. In practice that is three shots before you reach half the cap, and six shots already sits at it. More under coffee answers.
The number
| Shots | Standard espresso | Starbucks strength | Share of the 400 mg daily 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 | 94% |
The standard column uses 63 mg per 1 oz shot pulled from 7 to 9 g of grounds. Starbucks pulls a larger, longer shot at roughly 75 mg.
The last column is measured against the 400 mg per day the FDA describes as not generally associated with negative effects for healthy adults.
Where 400 mg comes from, and what it is not
The figure is the FDA’s, describing an amount not generally associated with negative effects in healthy adults. It is a population-level guideline, not a personal limit and not a threshold beyond which harm begins.
Two people at the same dose can have entirely different experiences, driven mostly by variation in the CYP1A2 enzyme that clears caffeine from the blood.
Some groups have lower published guidance. Pregnancy is commonly cited at 200 mg a day — three standard shots. Adolescents, people with heart arrhythmia and people taking certain medications are all advised lower.
None of that is captured by a single number.
Why this is a range, not a constant. Caffeine extraction depends on the bean, the dose, the grind and the length of the pull. Robusta carries roughly twice the caffeine of arabica by weight.
A ristretto pulled short from the same dose lands lower; a lungo pulled long lands higher. Treat every figure here as a planning number accurate to within about fifteen percent, not a laboratory result.
How it compares
| 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 |
The surprise for most people is the drip row. A single espresso is a concentrated shot, but a mug of filter coffee is a far larger volume — and it wins on total caffeine nearly every time.
A practical daily budget
| Pattern | Espresso total | Room left in the 400 mg cap |
|---|---|---|
| One double, morning only | 126 mg | 274 mg — plenty |
| Two doubles, morning and midday | 252 mg | 148 mg — a mug of tea still fits |
| Three doubles | 378 mg | 22 mg — nothing else caffeinated |
| Four doubles | 504 mg | over by 104 mg |
When you drink it matters as much as how much
Caffeine has a half-life of roughly five to six hours in a healthy adult, meaning half of what you drink at 4pm is still circulating at 10pm.
That is the mechanism behind the common complaint that “caffeine does not affect me, but I sleep badly” — tolerance builds against the alertness effect far faster than against the sleep disruption.
Genetics play a large part too. 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.
Common questions
What is a sensible cut-off time?
Work backwards from when you sleep, using a six hour half-life. For an 11pm bedtime, a last coffee at 3pm leaves roughly a quarter of it still circulating.
If you sleep badly and drink coffee after lunch, moving the cut-off earlier is the cheapest experiment available.
Does decaf count?
Barely. A decaf shot is roughly 3 to 8 mg. Six of them is under a single regular shot.
Should I count tea and cola?
Yes — the guideline is for total caffeine, not coffee. A black tea is about 47 mg and a cola about 34 mg, and those add up faster than most people expect across an afternoon.
Sources
- U.S. Food and Drug Administration — Spilling the Beans: How Much Caffeine is Too Much? (the 400 mg per day figure for healthy adults)
- U.S. Department of Agriculture — FoodData Central (caffeine content of brewed espresso and coffee)
Figures on this page are planning numbers, not measurements of your particular drink. Caffeine per shot varies with the bean, the dose, the grind and the length of the pull.
