A general rule for portions is 60 grams of coffee for every liter of water. Because mass is the most consistent way of measuring portions (as volume can change for coffee based on varietal and roast, and for water based on temperature), we suggest getting your hands on a digital scale. The more units of measure and load bearing capacity the scale boasts, the better. With a dependable scale it is easy to measure out 1.8 grams of coffee for every 1.0 fluid ounces of water you will be brewing with. If you do not have a scale available, use 3 level tablespoons of grounds for every 12 fluid ounces of water.
If you do find it necessary to make adjustments for your personal taste preference, try altering the particle size of your ground coffee rather than your portion.