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Mugs are a potter's bread and butter. According to The National Coffee Association and the Specialty Coffee Association of America, Americans consume 400 million cups of coffee every day, and there are 300 million people in America, which means that every American needs an average of 1.33 coffee mugs. So if every single person needs one (and a third) good mug, then every potter should have at least one solid mug in their repertoire.
The two main factors in making a good coffee mug are volume and comfort. Everyone has their own idea of how much coffee is the right amount of coffee in the morning, and everyone has their own way of holding a coffee mug comfortably. If you are about to throw your first mug (or your first anything for that matter) then think about your own personal preferences (and read our beginner's guide to throwing).
A small coffee from most chain stores is 12 oz, a medium is 16 oz, and a large is 20 oz. A standard coffee mug is 11 oz. How much do you drink at once?
Let’s assume your morning coffee is a 12 oz to-go cup, which is 4.25” tall, and 3.25” wide at the mouth. It sounds all well and good to throw a cylinder 4.25” tall and 3.25” wide, but as clay dries, it shrinks, and when it's fired it shrinks again, and when its fired to glaze it shrinks one more time. When all is said and done your mug could shrink up to 15%, and that doesn't sound like much, but a 4.25” tall mug will shrink to 3.61”. That's a lot of coffee to deny yourself in the morning.
To make up for the difference, multiply your desired height by 1.17. Now to make a 4.25” tall coffee mug, you really have to make a 4.97” tall one, so let’s just say 5” coffee mug.
Note: to calculate the right height for clay with different rates of shrinkage use this formula
Everyone's hands are a little different, so everyone likes to hold things a little differently. The makers of mass-produced coffee cups would have your believe that there is but one kind of handle and we should all accept that and drink our coffee like the rest of the world. Potters know better. Hands should not conform to coffee cups. Our morning coffee may be the last warm sip of comfort before stepping out into an otherwise cold and uncaring world. Our mugs should fit our hands better than a glove.
Unfortunately, there is no simple formula to tell you how to make a comfortable handle, and only trial and error will teach you, but here are some suggestions to point you in the right direction: a good handle should have ample room for 2 fingers to be looped through, somewhere for your thumb to rest and a curve to conform to the inside of your hand, so be generous with the proportions. Don't be afraid to attach the handle at the very top or very bottom of the mug and make it bigger than you think it should be because it will shrink.
Now that you are well on your way to mastering the functionality of your coffee cup, it’s time to start thinking about the style - the look that tells the world that this is your mug. Your style might be expressed in the shape, color or decoration, or some combination of the three.
Experiment as much as you can. With 400 million cups of coffee being drunk every day, chances are you know a lot of people who need a coffee mug.