When people talk about having “a cup of coffee,” they don’t necessarily mean 8 ounces (236 milliliters). For example, many people go for the large size of coffee at McDonald’s restaurants and Starbucks, at 20 ounces (591 milliliters). Or at home, they may have a 12- to 16-ounce mug.
The amounts of caffeine in larger drinks are usually considerably greater than in smaller servings, if the type of coffee bean and method of preparation are uniform.
So when you read guides online that say an 8-ounce cup of drip java has about 163 mg of caffeine, you can more than double the amount of the stimulating chemical for a 20-ounce size.
Drip coffee is the kind that drips through a filter to produce that cup or mug of the elixir that so many people say they can’t start their day without.
Other types of coffee include percolated, espresso, Turkish or Greek brewing, and French press.
The amount of caffeine in each drink varies, and caffeine intake also varies by the amounts of coffee people drink. Some gung-ho caffeine fanatics might scoff at a dainty 8-ounce portion while guzzling a 20-ounce cup of extra dark.
there is no such thing
as too much!
Join me… pic.twitter.com/aPKxFbnzCn
— Paul (@Loverdesart) February 8, 2016
Caffeine Informer gives the following amounts of caffeine for various brewed 8-ounce cups of the invigorating beverage:
• Filter or drip variety varies from 115 to 175 milligrams, for an average of 145 mg.
• French press or plunger ranges from 80 to 135, for an average of 107.5 mg.
• Percolated coffee varies from 64 to 272 mg and has an average of about 200 mg.
• Boiled Greek or Turkish coffee ranges from 164 to 240 and has an average of about 200 mg.
These amounts vary based on how the type of coffees in the product and how they are blended, how much coffee grounds a person uses to make a pot or cup of coffee and, of course, the brewing technique.
Espresso, in a cup 1.5 to 2 ounces, contains about 100 mg of caffeine. Instant coffee has about 65 to 100 mg of caffeine per 7 ounces. Decaffeinated coffee still has caffeine, but in negligible amounts less than 10 mg to about 30 mg in a 20-ounce brew.
Caffeine Informer gives a list  of Starbucks beverages and their caffeine contents. We are reporting this not to favor Starbucks but rather to show how coffee beverages differ in their caffeine content.
For example, a Caffe Latte has about 75 mg of coffee in 12 ounces (355 ml), Latte Macchiato has about 150, and Caffe Mocha has about 95. Cappuccino and espresso from Starbucks have about 75 mg, as does its Caramel Macchiato.
According to the Center for Science in the Public Interest , a 20-ounce cup of Dunkin' Donuts with Espresso Shot has 398 mg of caffeine. Compare that to Starbucks Cafe Americano, 16 ounces, with 225 mg of caffeine.
Graphic by CSPI
There are two main types of coffee beans in coffee you buy at the store or restaurant these days—Arabica and Robusta or Canephor. Both are grown in the many coffee-growing regions around the world. Arabica is in about 70 percent of coffee beverages, says Coffee.org . And Arabica has less caffeine than Robusta, as a person might figure from the root word “robust,” which means strong.
Coffee.org says Arabica is highly flavorful.
Robusta beans contain less oil and therefore taste more acidic and bitter. It is also a cheaper bean and is blended into coffees that you buy in the grocery store to save producers money. Robusta beans contain at least 50 percent more caffeine than Arabica.
Most Arabica coffee measures 1.1 to 1.4 percent caffeine during the first use or extraction. After the water is dripped, poured or pressed through the grounds, some caffeine remains in the grounds.
It can be hard to determine what type of beans are in some popular coffees. Folgers doesn’t list the type of beans in its Classic Roast, for example, but leaf.tv says the brand has a mix of Arabica and Robusta .
The proportion of Arabica to Robusta in various blends changes as the prices of the various beans fluctuate, so it can be difficult to determine exactly what type of coffee you are drinking.
That said, many gourmet coffees explicitly tell on their packaging what kind of beans they use.
Coffee Detective provides a list  of the various varieties of beans and what their percentage of caffeine is. One of the most popular coffees in North America, Colombian, has high amounts at 1.37 percent, the website says. Tanzania Peaberry coffee beans have even more, at 1.42 percent. By contrast, Mocha Mattari from Yemen has only 1.01 percent of caffeine.
Some of the Arabica coffee beans or grounds (unblended) and their percentage of caffeine, in ascending order, include:
Ethiopian Harrar-Moka 1.13
Mexico Pluma Altura 1.17
Java Estate Kuyumas 1.20
Brazil Bourbons 1.20
Celebes Kalossi 1.22
Jamaican Blue Mtn/Wallensford Estate 1.24
New Guinea 1.30
Sumatra Mandheling-Lintong 1.30
Guatemala Antigua 1.32
Kona Extra Prime 1.32
Panama Organic 1.34
Costa Rica Tarrazu 1.35
Kenya AA 1.36
Colombia Excelso 1.37
Colombia Supremo 1.37
Indian Mysore 1.37
Some blends and dark roasts and their caffeine content by percentage include:
French Roast 1.22
Vienna Roast 1.27
Espresso Roast 1.32
Colombia Supremo Dark 1.37%
Various other products contain caffeine, including tea, sodas and chocolate, but the main source of the caffeine that people ingest in the world is coffee.
|Starbucks Chai Latte—iced or regular||grande, 16 oz.||95|
|Starbucks Green Tea Latte—iced or regular||grande, 16 oz.||80|
|KeVita Master Brew Kombucha||15.2 oz.||36-68|
|Honest Tea Organic Lemon Tea||16 oz.||63|
|Tazo Organic Iced Black Tea, bottled||13.8 oz.||46-60|
|Gold Peak Unsweetened Tea||18.5 oz.||47|
|Green tea, brewed||8 oz.||28-38|
|Snapple Lemon Tea||16 oz.||37|
|Lipton Lemon Iced Tea||16.9 oz.||21|
|Arizona Iced Tea, black||8 oz.||15|
|Arizona Iced Tea, green||8 oz.||7.5|
|Lipton Decaffeinated Tea, black, brewed||8 oz.||<5|
|Herbal tea, brewed||8 oz.||0|
|Pepsi Zero Sugar||20 oz.||115|
|Mountain Dew—diet or regular||20 oz.||91|
|Diet Coke||20 oz.||76|
|FDA official limit for cola and pepper soft drinks||12 oz.||71|
|Pepsi Zero Sugar||12 oz.||69|
|Mountain Zevia||12 oz.||55|
|Mountain Dew—diet or regular||12 oz.||54|
|Diet Coke||12 oz.||46|
|Coca-Cola, Coke Zero, or Diet Pepsi||16 oz.||45|
|Dr. Pepper—diet or regular||12 oz.||41|
|Coca-Cola, Coke Zero, or Diet Pepsi||12 oz.||34|
|Pepsi True||10 oz.||32|
|Sunkist Orange Soda—diet or regular||20 oz.||31|
|Coca-Cola Life||12 oz.||28|
|Dr. Pepper—diet or regular||8 oz.||28|
|Barq's Root beer, regular||12 oz.||22|
|7-Up, Fanta, Fresca, ginger ale or Sprite||12 oz.||0|
|Root beer, most brands—diet or regular||20 oz.||0|
Chocolate Candy & Chocolate Drinks
|Crackheads Gourmet Chocolate Coffee Caffeine||1 box, 40 g||600|
|Crackheads Espresso Bean Candies||1 package, 28 pieces||200|
|Awake Caffeinated Chocolate Bar||1.5 oz.||100|
|Starbucks Hot Chocolate||16 oz.||25|
|Hershey's Milk Chocolate Kisses||9 pieces||10|
|Hershey's Milk Chocolate Bar||1.5 oz.||9|
|Hershey's Cocoa||1 Tbs.||8|
|Silk Chocolate Soymilk||8 oz.||<5|
|Silk Dark Chocolate Almondmilk||8 oz.||<5|
|Hershey's Chocolate Lowfat Milk||12 oz.||2|
Energy drinks vary from 300 mg of caffeine per 16-ounce can of Bang to 50 mg per 12-ounce can of Starbucks Refresher.
So is caffeine safe? Most probably, yes. Evidence is showing it may even be good for you.
What constitutes a normal amount of caffeine depends on the individual. Caffeine sensitivity depends on many factors, including the frequency and amount of regular intake, body weight and physical condition. Numerous studies have shown that moderate amounts of caffeine—about 300 milligrams per day—are safe for most adults. Some individuals may be sensitive to caffeine and will feel effects at smaller doses than do individuals who are less sensitive.
However much coffee you drink of whatever type, the wit Jilly Cooper has wise advice: “Never drink black coffee at lunch; it will keep you awake all afternoon.”
Unless you work outdoors or indoors in a job where you are physically active all day, it can be difficult for some people who have desk jobs to stay awake at work without caffeine.
Maybe the most important thing you can do to make sure you don’t nod off at work is to get a good night of sleep, at least 7 to 8 hours, at a regular time every night. Boredom can also cause you to nod off. Other than getting a good night’s sleep and having a fascinating job, there are things you can do to stay awake.
How do investment bankers stay awake on their 18-hour shifts?
Investment bankers work such long hours that many resort to chemical stimuli. There have been rumors of methamphetamine and cocaine use among investment bankers to burn the midnight oil. Other investment bankers take Ritalin or Adderall, which are given to children with ADHD but which are stimulants for adults. But the mainstay is probably coffee, energy drinks, and other concoctions containing caffeine.
Some law students spend 60 hours a week studying. Those who’ve been through law school advise prospective students to leave the Xbox at home so they’re not tempted with potentially ruinous distraction. How do law students get energy to study so much?
One thing many law school students do not do is party and socialize a lot. This has a doubly salutary effect because the time spent not partying is time they can spend studying. And then they are not out of sorts, hung over or over-tired the next day from partying.