the metabolism calculator likely is using the harris-benedict equation which is a method to estimate your basal metabolic rate (bmr) and daily calorie requirements. the variables that this equation takes into consideration are age height weight gender and activity level. keep in mind that this is an indirect method of calorie assessment and is only an estimate. there are other equations but this is typically the equation that most registered dietitians use.
webmd's metabolsim calculator. i have a book that uses weight in lbs x 11 x 1. 6 as the formula for caloric needs from basic daily activities. which gives me a much greater number then webmd's calculator. i am a 41 year old male. <link>