A typical 12 oz cup of brewed coffee contains roughly 120 to 144 mg of caffeine. That estimate scales from the widely cited Mayo Clinic figure of 96 mg per 8 oz cup, but the actual number in your mug depends on the beans, the roast, and where you bought it. Chain coffee shops often land well above that average.
Caffeine by Coffee Chain
Not all 12 oz coffees are created equal. Starbucks brewed coffee runs noticeably higher than competitors, packing 235 to 290 mg of caffeine in a Tall (12 oz) cup. That’s roughly double what you’d get from a home-brewed cup of the same size.
Dunkin’ and McDonald’s fall in a middle range. Dunkin’s small brewed coffee contains 180 mg in 10 oz, which works out to about 215 mg if you scale to 12 oz. McDonald’s McCafe lands in a similar neighborhood. Independent lab testing by Labdoor found that a medium McDonald’s coffee averaged 227 mg and a medium Dunkin’ averaged 220 mg, though those were tested at medium cup sizes rather than a strict 12 oz pour.
The takeaway: a 12 oz Starbucks can deliver nearly three times the caffeine of a 12 oz home brew, largely because Starbucks uses a higher coffee-to-water ratio and different bean blends.
Why the Number Varies So Much
Several factors push the caffeine count up or down within that same 12 oz serving.
Bean variety is the biggest one. The two main species of coffee bean, Arabica and Robusta, have very different caffeine levels. Arabica beans contain about 1.2 to 1.5% caffeine by weight, while Robusta beans pack 2.2 to 2.7%. Most specialty and home coffee is Arabica. Cheaper blends and instant coffees often include Robusta, which is one reason a budget cup can sometimes hit harder than you’d expect.
Roast level matters less than people think. Light roasts do contain slightly more caffeine than dark roasts because the roasting process breaks down a small amount of caffeine. One 2018 study found about 60 mg in a sample of light roast compared to 51 mg in the same amount of dark roast. But when coffee is measured by weight (as most cafés do), the difference is negligible. The old claim that dark roast is “stronger” refers to flavor intensity, not caffeine.
Brew method and ratio also play a role. A French press that steeps for four minutes extracts caffeine differently than a drip machine that runs water through grounds in two minutes. And simply using more grounds per cup, as many coffee shops do, raises the caffeine proportionally.
What About Decaf?
Decaf isn’t truly caffeine-free. A 10 to 12 oz cup of decaf brewed coffee typically contains 7 to 8 mg of caffeine. Starbucks decaf runs higher at around 20 mg per cup, while Dunkin’ and McDonald’s decaf clock in at 7 to 8 mg. Decaf instant coffee is the lowest at roughly 3 to 4 mg per serving. For most people these amounts are trivial, but if you’re highly sensitive to caffeine or drinking several cups of decaf a day, the milligrams add up.
How 12 Oz Fits Into Daily Limits
The FDA considers 400 mg of caffeine per day safe for most healthy adults. The agency describes that as roughly two to three 12 oz cups of coffee. If you’re drinking home-brewed coffee at around 120 to 140 mg per cup, three cups keeps you right at that ceiling. If you’re buying Starbucks Tall brews at 235 to 290 mg each, a single cup already accounts for more than half your daily budget, and two cups could push you over.
Caffeine takes about 30 minutes to kick in after you drink it, with a range of 15 to 45 minutes depending on the person. Its half-life in the body is 5 to 6 hours, meaning if you drink a 12 oz cup with 140 mg of caffeine at noon, roughly 70 mg is still circulating at 5 or 6 p.m. That’s worth keeping in mind if afternoon coffee tends to interfere with your sleep.
Quick Reference by Source
- Home-brewed drip (12 oz): ~120–144 mg
- Starbucks Tall, Pike Place (12 oz): 235–290 mg
- Dunkin’ brewed (scaled to 12 oz): ~210–215 mg
- McDonald’s McCafe (medium): ~227 mg
- Decaf brewed (12 oz): 7–20 mg