Site: http://www.preventdisease.com/healthtools/articles/bmr.html

Summary:

This calculator both you BMR (Basal Metabolic Rate) and AMR (Active Metabolic Rate).

BMR (Basal Metabolic Rate)

Your BMR, or basal metabolic rate (metabolism), is the energy (measured in calories) expended by the body at rest to maintain normal bodily functions. This continual work makes up about 60-70% of the calories we use ("burn" or expend) and includes the beating of our heart, respiration, and the maintenance of body temperature. Your BMR is influenced by a number of factors, including age, weight, height, gender, environmental temperature, dieting, and exercise habits.

AMR (Active Metabolic Rate)

To maintain normal bodily functions, your body "burns" more calories throughout the day than at rest. Once you have calculated your BMR above, you can enter the average minutes you spend in a variety of activities each day. This will help you calculate your AMR or Active Metabolic Rate. Your AMR is is the total amount of calories you expend through different types of activities throughout the day whether it's reading or walking, dancing or swimming. They keyword here is "active" meaning you are consciously aware of your activity. We have divided these into five levels (above) from very light to very heavy and included a few examples of each category to allow you to gauge where a given activity might fit. The result is only an estimate, but should give you an rough idea of your daily caloric needs. Once you've inputted all relevant fields, click the "Calculate" button to generate your daily "Daily Energy Requirement" which is the sum of your BMR and AMR results.