For 4 doses of the drink, I would pour together 1 1/2 cups of grapefruit juice and 1 1/2 cups of water (total 3 cups liquid). Then divide them into four equal portions which works out to 2/3 cups each. Then I put 600 mg. of magnesium citrate into each glass, stir before drinking.(or swallow capsules whole with each glass liquid instead, if you want to).Adjust amount of magnesium to your needs.