The size of "coffee cups" has changed so measurements are different. I just fill the pot and pour the water in the maker but we only get about 4 1?2 mugs of coffee.
Most coffee cups only hold about 6 ounces of coffee, mugs hold much more. Mugs are a relatively new coffee holder, meaning that when coffee pot standards were established many, many, many years ago everyone drank out of cups because all sets of dishes came with matching cups and saucers. Those cups held about 6 ounces of coffee, if you did not add cream. Today most people use mugs because they are decorative, souvenirs of a vacation, easier to pickup since they have larger handles, etc. So the coffee pot doesn't give as many mugs of coffee as it would cups of coffee.
I make coffee by boiling milk in a pan. I measure the amount of milk into two cups - exactly the right amount. Once the milk has boiled I pour it back into the cups but I always have about half a cup left over. Go figure!!
Is it a question of expanding molecules in the presence of heat (with/without the extra mass of coffee)? When I think about this problem, I first think in terms of mass, not volume. Volume and mass are two different things, naturally. When one adds coffee to water, this changes the mass of the pre-existing volume of water (as well as the volume). Even if you do not add coffee to the water...It is interesting to note that if you have a cup of warm water and a cup of cold water they both have the same number of molecules....the difference is that the molecules in the warmer cup of water are much more active (sort of bouncing around and off each other). I suspect that this can be expressed as "expansion". If one increases the temp, then the molecules become even more active and eventually the liquid can become steam .--the volumn is then expanded. This property of steam means that there is quite a bit of expansion...so much expansion that when enclosed in a weak container, there can be an explosion. I am not sure that this is the answer, but it is something to think about. Something else to think about is the fact that when water freezes it expands...I am not really talking about ice coffee here though. Think about a flower pot with soil and a plant that is left out-of-doors over the winter. If the outside temp drops below the freezing freezing point, the moisture in the soil will freeze and expand to such an extent that the pot can break. there are more factors to think about such as hard and soft water, heavy and light water as well as altitude. Water that boils and is not in a sealed container looses volume in the form of steam. The water expands, but evaporates--it is all very curious.
