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.
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.
And those variations are just for drip coffee. Other types of coffee include percolated, espresso, Turkish or Greek brewing, and French press. But drip coffee is the most common type in the United States, used in homes and many cafes, including McDonald’s, Starbucks and Dunkin Donuts, according to the website Caffeine Informer.
Coffee varies by the amount of caffeine in each drink and by the amounts of coffee each person drinks. 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 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. Cappucino and espresso from Starbucks have about 75 mg, as does its Caramel Macchiato.
There are two main types of coffee beans in coffee you buy at the store or restaurant these days—Arabic 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 them.
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. And the information is not readily available online.
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.
So is it safe? Most probably, yes. The International Food Information Council Foundation has a fact sheet here(PDF) that states:
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.”
As we said in this Viter Energy blog  about the work-life balance, it's a good idea to simulate your commute to work. You don't have to drive in to work, so instead take a walk around the block just before your workday starts and just after it ends. Send yourself a psychological signal.
And if you can avoid it, do not work after your walk around the block. Don't check work email. Don't answer calls from co-workers unless you really need to talk to them (or they are friends you socialize with).
Clinical psychologist Kelcey Stratton of Michigan Health Blog  has some sound advice on finding the right time to work:
If you’re a morning person, try to schedule important work and meetings during the first half of the day. Others may peak with energy in the afternoon. Depending on the type of job you have, try to maximize on these levels as you can.
The first bit of advice is to get up from the computer, turn off your phone, and go get some exercise, do something recreational, prepare a meal, or something other than work, on the same schedule as you did when you worked at the brick-and-mortar office.
If you used to get off at 5 p.m., quit working at home at 5. You might need to check email or prepare a report later that night, but be sure to get away from all electronic communications and computing devices for a while.
Another big tip is to take your coffee breaks and lunch breaks on the same schedule, or at least be sure to take them at some point. Do not skip your favorite part of the day!