While there’s probably no universal formula for eating to gain mass-after all a lot depends on your age, metabolism, level of activity, etc-there are some easy guidelines to keep in mind.
Overall, I’m not an advocate of extremely high calorie diets for natural bodybuilders; in all but the rarest cases, this usually results in the addition of too much bodyfat.
Assuming that you’re training and supplementing itelligently, here’s some general guidelines that should get you heading in the right direction:
Start by aiming to consume approximately 15 times your bodyweight in daily calories. So at a weight of 150 lbs you want to target approximately 2250 calories total per day.
Break up your calorie consumption into 5 or 6 relatively equal sized meals.
Feed your body high quality protein throughout the day, at least every 3 hours, to help support muscle growth. You’ll want to take in at least 1-2 grams of protein per pound of bodyweight.
If after 2-3 weeks you find you’re not gaining mass, up your calories by 250-300 per day.
You don’t need to overeat, but you do need to get your meals and your PROTEIN in. protein powdwers and other supplements can be a great help here.
Extract from musclemaster.com