A basal metabolic rate calculator determines the number of calories the body burns to perform basic human functions. It does not include any calories expended by exercise, or even by simply moving about. It will tell only the calories used if the subject were to remain in bed for an entire day. It can be useful to know this for weight management purposes.
The body constantly uses calories for bodily functions. Things like organ functions, hair and skin growth, and brain functions need calories to continue. This calorie usage is knows as the basal metabolic rate (BMR). It is sometimes also referred to as resting energy expenditure (REE).
A basal metabolic rate calculator attempts to discover what this rate of caloric usage is for an individual. The most basic calculator uses factors such as age, height, weight, and gender. More complex calculators add in overall activity level, since muscle mass and fitness can effect your caloric usage even while sleeping.
There are two equations that a basal metabolic rate calculator can use for operation, both varying slightly depending on the subject's gender. The Harris-Benedict Equation is the older of the two, and has been shown to be up to 5% inaccurate when dealing with overweight people. It is calculated as such:
- For men: BMR = 66 + (13.75 × weight) + (5.0 × height) - (6.76 × age)
- For women: BMR = 655 + (9.56 × weight) + (1.85 × height) - (4.68 × age)
The Mifflin Equation was first discussed in 1990, and has been shown to be a bit more accurate for determining an overweight subject's activity. It is calculated this way:
- For men: BMR = 5 + (10 × weight) + (6.25 × height) - (5 × age)
- For women: BMR = -161 + (10 × weight) + (6.25 × height) - (5 × age)
Both kinds of equations above require the weight to be expressed in kilograms, height in centimeters, and age in years. Therefore, a basal metabolic rate calculator that is calculated in pounds and feet must also have an equation written into it to properly convert the figures. Both the Harris-Benedict and Mifflin equations give results in the number of calories expended per day.
This number is most often used to calculate a caloric intake goal for someone who is attempting to lose weight. Dieters most often use a basal metabolic rate calculator in conjunction with a daily caloric calculator. This second calculator helps people to discover how many calories they burn through regular daily activities. The overall caloric intake goal should fall somewhere between these two numbers, if weight loss is the goal.