Bear in mind that the size of a standard cup of coffee is six ounces. Yes, six. This often bears no relation to the markings on your carafe. For example, I once had a coffee-maker that claimed to make 12 cups per pot, but a pot held 60 ounces of coffee, so in effect I was making 10 6-oz. cups. And so forth and so on.
So if your mug holds 8, 10, 12, or 15 ounces, you need to adjust your brewing amount according to the amount of brewed coffee you want to end up with. If you use one of those coffee scoops to measure the grounds, the proportion to start with is one level scoop for every six ounces of water, and adjust from there.