I have a "Mr Coffee" coffee maker. It is a "12-cup" capacity.  I put that in quotes because I use a 40 oz jar to fill it with water, and 2 40-oz jars is more than enough.  Calculations tell me it might be more of a 10-cup capacity.  I use a 1/4 cup of coffee in the coffee pot. Maybe some will think that seems weak, but it is strong enough for me.

Chris, just a little math here....

1 tablespoon = 3 teaspoons

1/4 cup = 4 tablespoons

I am using 1/4 cup for a 12-cup pot.  

Someone suggested 1 teaspoon coffee per 8 oz cup.

You are talking about 3 9-oz cups.  The way I do math.... I think 1 heaping tablespoon of coffee would be about right for your 3 cups.  At least, I would start there, and see how it turns out. You can adjust on the next batch as you need.