Using the HealthAssist calculator, a person weighing 80 pounds burns 50 calories in one hour if he is inactive, such as while sitting and reading or studying. An individual weighing 200 pounds burns the same amount of calories in less than 30 minutes.
Other fitness websites have calorie calculators that allow a person to factor in gender, height and age, which all play a role in the average speed of metabolism. For example, an older person generally burns fewer calories than a younger person while doing the same activity. Males tend to burn more calories than females due to higher average muscle mass even through everything else is the same with regard to weight, height and age.