Doofy,
50-30-30 refers to percentages of CALORIES, not bodyweight. First, you need to figure out how many calories you want to be eating, depending on your goals--loose, gain, or maintain weight.
I know you are trying to cut up--most people would tell you to multiply your weight by 10-12, but I think it is better to look at what you are eating now (if you are maintaining weight), and subtract 300-500 cals from that, or subtract 600-1000 cals if you are gaining.
For simplicity, lets say you figure you need to eat about 2000 cals a day to cut, and want to try this 50-30-20 diet.
2000 x .50 = 1000 cals of protein
There are 4 cals/gram of protein, so you need 1000/4 = 250 grams of protein per day.
2000 x .30 = 600 cals of carbohydrate
There are also 4 cals/gram of carbohydrate, so you need 600/4=150 grams of carbs per day.
2000 x .20 = 400 cals of fat.
There are 9 cals/gram of fat, so you need 400/9= 44.44 grams of fat per day.