Sleeping BMR Calculator

Understanding how many calories, per 24 hours, the body needs to support basal metabolic function helps create a weight plan either for maintaining or losing weight.

The BMR is defined as the minimum amount of energy that is required for vital body functions such as respiration or circulation, usually expended when resting or sleeping.

Please note that calories required for day to day activities and exercise come on top of the BMR and need to be accounted for separately.

Variables considered

There are two tabs with the same fields to input but different measurement units: English and Metric.

Height can be provided in ft and inches or centimeters while weight can be input in lbs or kg. Age and gender are also compulsory to be input because they are used in the calculation due to gender and age specificities of the basal metabolic rate.

Basal Metabolic Rate equations

The Harris-Benedict equations the sleeping BMR calculator uses have been adapted for English and Metric measurement use and are as follows:

■ English BMR:

Female BMR = 655 + (4.35 x Weight in lbs) + (4.7 x Height in inches) - (4.7 x Age in years)              

Male BMR = 66 + (6.23 x Weight in lbs) + (12.7 x Height in inches) - (6.8 x Age in years)

■ Metric BMR:

Female BMR = 655 + (9.6 x Weight in kg) + (1.8 x Height in cm) - (4.7 x Age in years)

Male BMR = 66 + (13.7 x Weight in kg) + (5 x Height in cm) - (6.8 x Age in years)

The original equations have been calibrated for the following:

■ Weight values between 25 and 124.9 kg (55 to 275 lbs);

■ Height values between 151 and 200 cm (60 to 79 inches);

■ Ages between 21 and 70.

About the original BMR study

The BMR equations originate in 1918 study conducted by James Arthur Harris and Francis Gano Benedict, which was published in 1919 by the Carnegie Institution of Washington in the monograph A Biometric Study Of Basal Metabolism In Man.

Measurements have been taken of 36 men, 103 women and 94 new-born infants and have been analysed biometrically to extract the standard constants. A correlation has been found between the basal pulse rate and the basal metabolism and also between body weight and heat production.

The study has also highlighted the change in basal metabolism with age.

The most common three prediction equations, beside the Harris-Benedict, are the Mifflin-St Jeor, Owen, and World Health Organization/Food and Agriculture Organization/United Nations University [WHO/FAO/UNU].

It is considered that the most reliable one is the Mifflin-St Jeor equation, created in 1990, that is present in the calorie calculator. Also, there are other basal metabolic rate equations which account for lean body mass.

BMR limitations

Factors such as stress, excitement or temperature can influence the body’s autonomous control of the metabolic rate, thus energy consumption can be increased or decreased around the BMR.

Given the fact that it does not account for body fat composition, any basal metabolic calculator based on the above formulas cannot be 100% accurate.

This is made obvious when comparing a person with a heavy muscular built (where the BMR underestimates their caloric requirement) and another person of the same weight but with a higher percentage of body fat (where the BMR will overestimate the number of calories needed).

Original reference

Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Proc Natl Acad Sci U S A. 1918; 4(12):370-3.

Validation study

Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005; 105(5):775-89.

Other reference

Speakman JR, Selman C. Physical activity and resting metabolic rate. Proc Nutr Soc. 2003; 62(3):621-34.