The Harris-Benedict formula is a relatively simple process in which a person multiplies their basal metabolic rate (BMR) by their average daily activity level.
BMR is the number of calories a person burns by simply existing. BMR varies based on age, sex, size, and genetics. To calculate BMR, a person uses inches for height, pounds for weight, and years for age in the following formulas:
For men: 66 + (6.2 x weight) + (12.7 x height) – (6.76 x age)
For women: 655.1 + (4.35 x weight) + (4.7 x height) – (4.7 x age)
The results of the BMR calculation are then used to multiply against the average daily activity of the person. Points are awarded based on how active a person is.
Points for activity levels are as follows:
1.2 points for a person who does little to no exercise
1.37 points for a slightly active person who does light exercise 1–3 days a week
1.55 points for a moderately active person who performs moderate exercise 3–5 days a week
1.725 points for a very active person who exercises hard 6–7 days a week
1.9 points for an extra active person who either has a physically demanding job or has a particularly challenging exercise routine
When the BMR is calculated and the activities points are determined, the two scores are multiplied. The total is the number of calories burned on an average day.
For example, to calculate how many calories a 37-year-old, 6-foot-tall, and 170-pound man who is moderately active burns, the formula would look like:
(66 + (6.2 x 170) + (12.7 x 72) – (6.76 x 37)) x 1.55 = 2,766 calories/day