How to Calculate Basal Metabolic Rate (BMR) and Daily Calorie Needs

Basal metabolic rate, aka BMR, is the base rate of metabolism in a human body. Your BMR represents the number of calories you would need to consume everyday if you did nothing but sleep. Of course, nobody sleeps 24 hours a day, so naturally your daily caloric intake needs will be higher than your BMR value. BMR is the starting point for calculating your calorie needs.

This article discusses two methods of determining your basal metabolic rate. The first uses weight, height, age, and activity level. The second uses weight, percent body fat, and activity level. The BMR calculator at left computes your BMR and daily calorie needs in kcal using the Revised Harris-Benedict Equation of Method 1.

Method 1: The Revised Harris-Benedict Equation

Measure your weight in kg, your height in cm, and your age in years. Call these variables W, H, and A. For men, the BMR formula is

BMR = 13.397W + 4.799H - 5.677A + 88.362

For women, the BMR formula is slightly different:

BMR = 9.247W + 3.098H - 4.33A + 447.593

Notice that in both BMR formulas, the age factors are subtracted. This means that the older you are, the fewer calories you need to maintain the basal metabolic rate.

(To convert pounds to kilograms, multiply by 0.4536. To convert inches to centimeters, multiply by 2.54.)

Now to estimate your daily calorie needs, take your BMR and multiply it by a factor that corresponds to your activity level.

little to no exercise: 1.2
exercise 1-3 times a week: 1.375
exercise 3-5 times a week: 1.55
exercise almost everyday: 1.725
extreme fitness regimen: 1.9

Method 2: Katch-McArdle Lean Body Mass Equation

The alternative method for computing BMR is based on weight and percent body fat. Let W equal your weight and let P equal your percent body fat P, expressed as a decimal (31% = 0.31). Then use either of the following two formulas:

BMR = 370 + 9.798W_lbs(1-P)       (weight in pounds)

BMR = 370 + 21.6W_kg(1-P)       (weight in kilograms)

If you know your lean body weight, you can replace the W(1-P) factor with your lean body weight instead. To determine your daily caloric intake, multiply your BMR by one of the factors given in Method 1.

Here are some examples to illustrate the two methods for computing BMR. Suppose Bill is 40 years old, 160 lbs, 70 inches tall, and 23% body fat. And suppose Jenny is 37 years old, 140 lbs, 66 inches tall, and 29% body fat. With the first method, their basal metabolic rates are

Bill's BMR = 998.4 + 889.7 - 270.4 + 66.47 = 1684.17
Jenny's BMR = 607.6 + 310.2 - 173.16 + 655.1 = 1399.74

With the second method, their BMRs are

Bill's BMR = 370 + 9.795(160)(0.77) = 1576.74
Jenny's BMR = 370 + 9.795(140)(0.71) = 1343.62

As you can see, the values are similar for both methods. You can use whichever method you prefer, or average the 2 results.

© Had2Know 2010