How many cups of coffee can you brew from a 12oz bag?
The amount of cups of coffee you get from a 12-ounce bag totally depends on a number of factors.
1) What are you calling a "cup?" They range in size. An 8 ounce cup is a lot smaller than a 17 ounce cup (duh) (leave room for cream!).
2) How many grounds are you scooping into the mix?
3) What sort of grind are you using?
4) What sort of roast are you using?
5) What sort of BEAN are you using?
6) How strong of a brew do you like?
Those factors, and probably a few others, will dictate what yield you get from a bag of coffee.
So...there is not a universal answer to this question!
Do your homework and take your time. Measure your cups and your brews. Write down and track your mixes and what you do and don't like. Quite likely, the ratio and yield for a 12-ounce bag of beans will be around 18 - 22 cups.
HINT: When you near the end of the pot, don't be afraid to pour the leftovers into a bottle and keep that bottle in the fridge. Some drinkers just MIGHT want to warm that up one morning instead of starting a fresh pot. Others might add some ice to it and enjoy an afternoon vacation in the shade. Still others might mix it with batter for a coffee flavored pastry dish. The bottom line: NEVER pour it down the drain!