BMR Calculator (Harris-Benedict)
Estimate basal metabolic rate using the 1984 revised Harris-Benedict equation.
What this tool does
This calculator estimates basal metabolic rate (BMR) using the 1984 revised Harris-Benedict equation published by Roza and Shizgal. It requires weight, height, age, and biological sex as inputs, then applies sex-specific formulas to estimate daily resting energy expenditure in kilocalories. The equation was derived from studies of healthy adults and provides a population-average estimate of the calories the body burns at complete rest to maintain vital functions.
Formula Used
Disclaimer
This calculator is for educational and informational purposes only. It does not provide medical, nutritional, or training advice. Results are mathematical estimates and may not reflect individual circumstances. Consult a qualified coach, registered dietitian, medical professional, or physiotherapist for personal guidance.
This calculator applies the revised Harris-Benedict equations published in 1984 to estimate basal metabolic rate: the number of calories the body expends at complete rest to maintain vital functions such as respiration, circulation, and cellular metabolism.
How BMR Calculator (Harris-Benedict) works
The tool accepts weight in kilograms, height in centimetres, age in years, and biological sex, then applies sex-specific linear regression equations derived from indirect calorimetry studies. The revision it uses was published by Roza and Shizgal in 1984, recalculating the original 1919 coefficients against updated measurement data. The output is an estimate of daily energy expenditure at rest, expressed in kilocalories per day.
The formula
Male: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
Female: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)
Worked through: a 30-year-old man at 75 kg and 175 cm (about 165 lb and 5 ft 9 in) comes to 88.362 + 1,004.775 + 839.825 − 170.31 = 1,762.7, which the tool reports as 1,763 kcal, roughly 7,375 kJ for readers whose labels use kilojoules. A 34-year-old woman at 68 kg and 168 cm comes to 1,449.6, reported as 1,450 kcal. Enter weights in pounds or heights in feet and inches through the unit toggle; the equation itself always runs in metric.
Where this method is most accurate
The revised Harris-Benedict equations were derived primarily from healthy adults of European descent measured under controlled laboratory conditions. Accuracy tends to be highest for individuals with body compositions near population norms. The equations do not account for variations in lean mass percentage, metabolic adaptation, thyroid function, or genetic polymorphisms affecting metabolic rate, and measurement error in the inputs propagates directly into the estimate. In Frankenfield's 2005 systematic review, Harris-Benedict tended to overestimate measured resting metabolic rate, and the Mifflin-St Jeor equation landed within 10% of measurement more often; both remain population models rather than individual measurements.
What this tool does not do
This calculator does not provide total daily energy expenditure; it estimates resting metabolism only. It does not account for physical activity, thermogenesis from food digestion, or non-exercise activity thermogenesis. It does not generate meal plans, macronutrient targets, or training recommendations. The output is a population-derived estimate, not an individualised assessment of metabolic health or a substitute for indirect calorimetry or doubly labelled water measurement.
Disclaimer
This tool is provided for educational and informational purposes only. It is not medical, nutritional, or training advice. The calculator implements a published equation; individual metabolic rates vary. Consult qualified professionals before making decisions related to nutrition, exercise programming, or health management.
Questions
- What is the difference between the original and revised Harris-Benedict equations?
- The original Harris-Benedict equations were published in 1919 based on indirect calorimetry of 136 men, 103 women, and 94 infants. The 1984 revision by Roza and Shizgal recalculated the coefficients using updated data and statistical methods, resulting in different intercept and slope constants for both male and female formulas.
- Why does BMR decline with age in the formula?
- The negative age coefficient reflects the population-level trend of declining lean body mass and reduced cellular metabolic activity with advancing age. The equation incorporates a fixed age penalty of approximately 5.7 kcal/day per year for males and 4.3 kcal/day per year for females, derived from cross-sectional regression analysis.
- How does this differ from the Mifflin-St Jeor equation?
- The Mifflin-St Jeor equation was published in 1990 using a larger, more contemporary sample. For the worked examples on this page it comes out about 3.5% lower than Harris-Benedict (1,699 versus 1,763 kcal for the same man; 1,399 versus 1,450 kcal for the same woman), and Frankenfield's 2005 review found it lands within 10% of measured resting metabolic rate more often. Both are population-derived linear models; neither directly measures individual metabolic rate.
- Can this estimate be used for total daily energy expenditure?
- No. BMR represents resting metabolism only. Total daily energy expenditure requires multiplying BMR by an activity factor (often 1.2 to 2.0) to account for physical activity, the thermic effect of food, and non-exercise activity thermogenesis. This calculator returns only the basal component.
- What measurement conditions does the equation assume?
- The Harris-Benedict equations assume standard indirect calorimetry conditions: post-absorptive state (8–12 hours fasted), supine rest, thermoneutral environment, and absence of acute illness or psychological stress. Real-world measurements taken under different conditions may deviate from the estimate.
Sources & Methodology
Applies the 1984 revised Harris-Benedict equations (Roza & Shizgal, Am J Clin Nutr 1984). Males: 88.362 + 13.397×weight_kg + 4.799×height_cm − 5.677×age. Females: 447.593 + 9.247×weight_kg + 3.098×height_cm − 4.330×age. Estimates basal metabolic rate from anthropometric data.
- › Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-82.
- › Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Proc Natl Acad Sci U S A. 1918;4(12):370-3.
- › Frankenfield D, et al. 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.
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