How many calories should I consume?

To determine your approximate caloric needs, you can easily compute your basal metabolic rate. This is the number of calories your body needs to maintain its basic functions and your current weight. You can determine your BMR by multiplying your current weight by 10. For example, if you weigh 180 pounds, then eating 1,800 calories a day would be your BMR.

However, this computation doesn't take into account exercise or your activity level. For example, since someone who exercises regularly can bring in more calories and still be at their maintenance weight, their BMR would be higher. Other issues like genetics, age and the amount of body fat/muscle you have can also affect your caloric needs.

Resource:
http://weightloss.about.com/cs/nutrition101/l/blcalories.htm