Calories and Gaining Muscle Mass

I'm a huge fan of weightlifting and am very proud of my definition, etc. but I know that to truly gain muscle mass you have to eat more -- but just how much more??

Like, 250 calories per day or 500 per day? I know that WHEN you eat also plays an integral part so I'm diligent about that as well.

Hints and tips, please?

I don't know if there is a "set" number, but protein is critical.  I literally "snack" on grilled chicken breast during the day.  After a workout I like to have a protein heavy meal, and I will also tend to have my carb 'o the day with that meal.....for instance, tonight I'll do P90X and then I'll have spaghetti and meatsauce (1/2 cup whole grain noodles with a cup of marinara/90% lean ground beef sauce (mostly meat)).

I also eat a protein "snack" about 20-30 mins  before I workout like hard cheese or nuts.

I'm eating around 1,500-1,800 calories per day with 140 grams of protein and about the same in carbs.  Maintaining at goal for 15 months now, and I workout 6x a week mixing cardio (running) with weights.

I have good definintion and muscle tone all over (although  I can't see the core muscles because of the skin!) and don't desire to bulk up any more.  I had to cut back on my HIIT because my legs were getting bigger and the legs on my jeans were getting tighter!

If you believe the -3500 cals you lose a pound then it would be +2000 cals to gain a pound of muscle. I am not sure I buy it though. There are days I eat all day and I'm not putting a pound of muscle on on those days. It took me over a year to gain 35 pounds of muscle.

I think you need to up the intake but do it slowly and see how your body reacts. Protein is key but you also need more carbs. I try to consume most of my carbs pre and post workout.

I now eat to my hunger. So, when I lift heavy, I am starving and eat more and gain muscle (and some fat). I don't actually keep track of how many calories though.