In order to build muscle, the number one requirement is that you eat more calories than it takes to maintain your weight. If you do not do this, it is literally impossible to build new muscle tissue since you are not supplying your body with the extra building blocks to form this muscle tissue.
Generally speaking, to build muscle at a rate of one pound a week, you should be consuming an extra 500 calories per day. This will translate to a total of 3500 calories, which is what it takes, on average, to generate one pound of body tissue.
Remember though, this is not one pound of solid muscle, as you will gain some fat during the muscle building process, but, if you're smart with how you go about building muscle, you can control how much extra fat is gained.
Doing A Slow Bulk
One option that some guys use is a much slower approach to building muscle. This is when they eat a smaller amount of calories over what they require to maintain their weight in hopes that this will prevent them from earning all that much fat.
While this can be a good idea in some cases, if you are only eating an extra 100 calories over your maintenance level, you may find that your progress is incredibly slow or almost non-existent.
For some people, when their body is faced with a small amount of excess calories, it just speeds up to accommodate this extra rather than actually using these extra calories to gain weight. This is what is know as a 'thrifty' metabolism and usually what makes a 'hardgainer' a 'hardgainer'.
Upping this small excess amount to around 250 extra would be a good way to hopefully get this situation as it'll give you enough extra that your metabolism should just catch up, while still minimizing the amount of fat you put on.
At 250 calories, this will have you putting about about p pound a week, which is about the max amount of lean muscle tissue you could build each week (assuming an ideal training environment).
Stepping It Up
Then, for those of you who are not afraid of gaining a little fat and would just like to speed up the whole process, you could potentially step it up to a maximum of 1000 calories over what you take to maintain your weight. Note that I would not go higher than this, because then you really will be putting on unneeded amounts of fat.
This is a big problem that many do face. They adopt a 'see-food' type of diet – where they pretty much eat everything in sight. While this will definitely get you putting on weight, unless you plan to devote a few months after the muscle building period is over to dieting, this is not advisable. You should still keep your overall health in mind and eating a great deal of junk food is not going to maximize a nutritional status.
For some individuals who really struggle to gain weight, you will need to approach that 1000 calories over value in order to see noticeable gains, however.
Also, do not be surprised if you do progress onwards with your weight gain you need to keep increasing the amount of calories you need to eat to continue to gain weight.
Remember, as you continuously build new muscle, this muscle tissue will be metabolically active and as such, your calorie requirements just to maintain your weight will also go up.
So, keep these points in mind when trying to determine which type of approach you want to take when it comes to your quest to build muscle.