Step one:

Decide what your metabolic rate is-slow, moderate, or fast.
If you think you have a pretty slow metabolism, multiply your current body­weight by 12.
If you think your metabolic rate is somewhat moderate, multiply your current bodyweight by 15.
If you think your metabolism is fast, multiply your current bodyweight by 18. For example, if a bodybuilder weighs 200 Ibs and has a moderate metabolism, the equation would be 200 x 15 = 3,000.

Step two:

If you decide to follow a diet that consists of 30% protein, 50% carbs, and 20% fat, plug them into the following formula.
Protein: 3,000 calories x .30 (30%) = 900 protein calories divided by 4 = 225 grams of protein per day.
Carbs: 3,000 calories x .50 (50%) =1,500 carbohydrate calories divided by 4 = 375 grams of carbs per day.
Fat: 3,000 calories x .20 (20%) = 600 fat calories divided by 9 = 67 grams of fat per day.

Step three:

Now divide your calories and total grams of fat, protein, and carbs by the number of meals you’ll be eating each day. In the case of most body­builders, it should be six meals per day.
So, for example. 3,000 calories divided by 6 (meals) = 500 calories per meal.
225 grams of protein divided by 6 = 37.5 grams of protein per meal.
375 grams of carbs divided by 6 = 62.5 grams of carbs per meal.
67 grams of fat divided by 6 =11 grams of fat per meal.

This formula can be used to determine any macronutrient balance, whether it’s 30/40/30 or 30/50/20.
Some people eat more carbs earlier in the day, while others spread them out evenly. Each individual needs to decide what works best for him or her.