A bag of coffee will say "X Tablespoons makes Y cups", and mean 6 oz cups.
In trying to back up your claim for you, I checked three brands of instant coffee: Folgers, Nescafe, and Maxwell House (chosen because they were the brands I saw when searching Amazon for "instant coffee"). Folgers provides a website full of coffee-related recipes. Here are a few:
http://www.folgerscoffee.com/coffee-how-to/how-to-make-coffe...
"How to make coffee" tells us that a single-serve coffee packet should be added to "6 fluid ounces" of water (or optionally, milk).
http://www.folgerscoffee.com/coffee-how-to/how-to-make-coffe...
"How to make coffee (in a coffee maker)" tells us that a "serving size" is "6 fluid ounces", and that however much water you put in to the coffee maker, you should add about 1 tablespoon of coffee per 6 oz water for mild coffee and double that for strong coffee.
http://www.folgerscoffee.com/coffee-how-to/how-to-measure-co...
"How to measure coffee" makes no particular recommendation on serving sizes, but implies that natural measurement amounts are "6 fluid ounces", "30 fluid ounces", and "60 fluid ounces" of water.
http://www.folgerscoffee.com/coffee-drink-recipes/vanilla-la...
"Vanilla Latte", a recipe which includes brewed coffee as an ingredient, calls for "1/2 cup milk" and "1/4 cup" brewed coffee. If we assume they're still thinking that 6 oz is a natural serving size, then 1/4 cup of brewed coffee is, according to the folgers people, 2 fluid ounces. In fact, they have several different recipes under different categories ("latte", "mocha", "cappuccino"...) all of which call for (1) 1/2 cup milk; (2) 1/4 cup either water or brewed coffee; and (3) a generous dollop of flavoring, usually syrup.
I didn't find any single-serving recipes for Nescafe or Maxwell House (or Kraft, which owns Maxwell House), so I looked at the packaging:
http://www.amazon.com/Maxwell-House-Roast-Ground-Coffee/dp/B...
Maxwell House helpfully informs us that coffee should be mixed one tablespoon of coffee to one "serving" of water, or 8 tablespoons of coffee to ten "servings" of water. They also note, "1 serving of water is 6 fl oz (3/4 cup)".
http://www.amazon.com/Nescafe-Classic-Instant-Coffee-Ounce/d...
Nescafe says "Use 1 heaping teaspoon of coffee per cup". However, it is immediately apparent that "cup" is not a measurement, because step 2 is "Pour 6 oz hot water over coffee".
But wait! I did find a coffee recipe ("Pumpkin spice latte") on Kraft. It's multiple-serving, which is the ideal case for an instruction of the form "Mix X T of coffee with Y cups of hot water". But here are the relevant ingredients:
1. "1/2 cup GEVALIA House Blend"
2. "1 qt. (4 cups) water"
There's no way to interpret those cups as being 6 ounces, since 4 of them make a quart.
In sum, you have no clue what you're talking about. Where did you get this idea, and why are you polluting the comments with it?
I just bought a measuring cup set here in Japan and the 1 cup measure is 255ml.
If that's not bad enough, a "cup" is 150ml when measuring coffee and 180ml when measuring rice.
Unfortunately, "cup" is not a standard measurement. :)
The (rarely used) UK Cup 284ml, and the Japanese Cup is 200ml.
If you don't live in the US and get a random recipe book, these differences are confusing.
Other factors likely to be (more) important: (a) Measuring dry ingredients by volume (b) The specific sub-type/quality of ingredient used.
American; never heard of such a thing. There's a unit of volume called "cup", and it's the same (~237 mL) everywhere.
We measure spices by volume, not weight: 1 cup = 16 tablespoons ("tbsp"); 1 tablespoon = 3 teaspoons ("tsp").
A liter is about a quart and there's 4 cups per quart so figure a cup is about 250 mL volume. Or a half cup would be about 125 mL, etc.
WRT liquid most medical types like to think a teaspoon is about 5 mL and a tablespoon is three teaspoons aka 15 mL.
Good luck with pastry and cake recipes, those require real precision. Everything else, just get the ratios about right and you'll be fine.
Unbelievable. Surely at some point someone must have realised thats a terrible idea?
A fluid Oz is 1/16 of a pint.
An oz of weight is 1/16 of a pound.
A pint of water weights 1 pound ("A Pint's a Pound, the World Around").
Aside: I actually like the customary system for fluid measurements; it's based on halves and as such is divisible by eye, not requiring graduations.
Or 1/12 of a pound, though, to be fair, I don't think anyone uses troy ounces in recipes.
> They are equivalent for water, almost equivalent for most liquids, and not equivalent for most solids.
Even solid foods are often right around the same density of water, so its often quite close for solid foods. (And, usually, if volume is intended rather than weight, listings will specify fluid ounces.)