What Is the Harris–Benedict Equation?
The Harris–Benedict Equation is one of the most historically foundational mathematical models in human energetics and nutritional science. First published between 1918 and 1919 by American biometrician J. Arthur Harris and physiologist Francis G. Benedict at the Carnegie Institution of Washington, the equation predicts Basal Metabolic Rate (BMR)—the minimum 24-hour caloric expenditure required to maintain essential bodily functions at complete physical rest.
Prior to Harris and Benedict's work, basal metabolism could only be estimated through cumbersome direct or indirect calorimetry chambers. By applying multivariate linear regression across body weight, stature (height), age, and biological sex in 239 healthy adult subjects, Harris and Benedict established the world's first standardized predictive formula for human metabolism.
Original (1919) vs. Revised (1984) Harris–Benedict: Why It Was Reevaluated
Many online calculators refer vaguely to “the Harris–Benedict formula” without specifying which version they use. In modern nutritional science, there are two distinct versions:
Original Harris–Benedict Equation
Derived from 136 men and 103 women. While groundbreaking, the original equations used a very high base constant (655.1 kcal) and low height multiplier (1.85 kcal/cm) for women, which modern studies found tended to underestimate BMR in taller women and overestimate in older individuals.
Revised Harris–Benedict Equation
Published in The American Journal of Clinical Nutrition by A. M. Roza and H. M. Shizgal (PMID: 6741850). The researchers reanalyzed the Carnegie database alongside modern measurements of Body Cell Mass (BCM) and total exchangeable potassium, recalibrating the coefficients to improve scaling across height and body composition.
💡 The Signature Difference on TDEE.page:
Unlike other calculators that silently mix coefficients or hide their formula version, TDEE.page explicitly separates both equations and provides a live, side-by-side comparison of the mathematical delta between the 1919 original and the 1984 Roza–Shizgal revision.
Complete Harris–Benedict Equation Reference Table
Exact mathematical specifications for both historical (1918/1919) and revised (1984) formulas.
| Sex | Version & Citation | Mathematical Equation (kcal / 24h) | Dataset Details |
|---|---|---|---|
| Men / Males | Revised (1984) Roza & Shizgal | BMR = 88.362 + 13.397W + 4.799H - 5.677A | Calibrated with modern Body Cell Mass (BCM) |
| Original (1918/1919) Harris & Benedict | BMR = 66.473 + 13.7516W + 5.0033H - 6.755A | Original 136 young adult male subjects | |
| Women / Females | Revised (1984) Roza & Shizgal | BMR = 447.593 + 9.247W + 3.098H - 4.330A | +1.25 higher height scaling for taller women |
| Original (1918/1919) Harris & Benedict | BMR = 655.0955 + 9.5634W + 1.8496H - 4.6756A | Original 103 adult female subjects |
Notation: W = body weight in kilograms (kg); H = body height in centimetres (cm); A = age in full years.
BMR vs. RMR vs. TDEE: Understanding Physiological Boundaries
In fitness literature, terms like BMR, RMR, and TDEE are frequently used interchangeably. However, they represent distinctly different metabolic conditions:
| Metabolic Metric | Physiological State | Measurement Conditions | Proportion of Total Burn |
|---|---|---|---|
| BMR (Harris–Benedict Output) | Basal Metabolic Rate | Strict 12h overnight fast, post-sleep awakening, thermo-neutral room, zero movement. | ~60–70% of TDEE |
| RMR / REE | Resting Metabolic Rate | Resting seated/supine in a controlled setting, 4–5h post-meal. Typically 3–10% higher than BMR. | ~65–75% of TDEE |
| TDEE | Total Daily Energy Expenditure | Full 24h expenditure: BMR + Physical Activity (PAL) + Thermic Effect of Food (TEF) + NEAT. | 100% of Daily Output |
How Accurate Is the Harris–Benedict Equation?
While some commercial websites advertise Harris–Benedict as “the most accurate BMR formula,” peer-reviewed scientific research demonstrates that all predictive equations carry inherent statistical variance:
📊 Statistical Precision
In their 1984 reevaluation, Roza & Shizgal reported a 95% confidence interval of ±213 kcal/day for men and ±201 kcal/day for women (~14% precision in healthy individuals). In non-standard population groups, predictive accuracy may vary.
🔬 Systematic Review Comparison
A comprehensive systematic review (Frankenfield et al., 2005) found that while Harris–Benedict is a reliable mathematical model, the Mifflin–St Jeor equation (1990) predicted resting energy expenditure within 10% of measured calorimetry in a higher percentage of modern individuals.
⚠️ Responsible Interpretation:
Your calculated BMR is a predictive statistical estimate, not a biological laboratory measurement. True individual metabolism fluctuates based on lean body mass, spontaneous daily movement, and prior nutritional history.
Why Does My Harris–Benedict Result Differ on Other Websites?
If you have entered your numbers into different online calculators and received varying outputs, the discrepancy usually stems from one of four technical factors:
- Original 1919 vs. Revised 1984 Version: Many websites run the 1919 equations while others use the 1984 Roza–Shizgal revision, causing a 20–60 kcal variance without labeling which version was selected.
- Rounding of Coefficients: Some calculators round constants heavily (e.g. using 13.4 instead of 13.397, or 66.5 instead of 66.473), creating small arithmetic drift.
- Imperial Unit Conversion Timing: Converting pounds to kilograms at 2.2 vs 2.20462, or converting height before or after rounding, shifts final numbers by 5–15 kcal.
- Conflating BMR with TDEE: Some tools apply hidden activity factors (such as 1.1 or 1.2) by default, displaying a total maintenance number rather than true basal metabolism.
Youth & Special Population Considerations
The standard Harris–Benedict equations were parameterized and validated on adult populations ($\ge 18$ years). In youths and teenagers, natural biological growth adds substantial energy demands that adult regression equations do not capture.
Standard adult BMR equations should not be used to set restrictive targets for growing youths, or pregnant/lactating individuals without guidance from a qualified professional or guardian.
Frequently Asked Questions About Harris–Benedict
What is the difference between original and revised Harris–Benedict?▼
The original 1918/1919 equation was derived by Harris & Benedict from 239 subjects. The 1984 revision by Roza & Shizgal recalibrated the coefficients using modern determinations of Body Cell Mass (BCM). The 1984 revision notably increased the height multiplier for women from 1.85 to 3.10 kcal/cm, resolving an underestimation issue in taller women.
Which Harris–Benedict equation should I use?▼
We recommend using the Revised 1984 Roza–Shizgal equation because it reflects modern dataset calibrations. However, we also provide the 1919 original for historical comparison.
How does Harris–Benedict compare to Mifflin-St Jeor?▼
Mifflin-St Jeor was developed in 1990 and is recommended by the Academy of Nutrition and Dietetics for general healthy adults. Harris–Benedict tends to estimate 20–60 kcal higher than Mifflin-St Jeor because its historical cohorts were leaner on average.
Does Harris–Benedict calculate BMR or TDEE?▼
Harris–Benedict strictly calculates Basal Metabolic Rate (BMR)—your resting energy baseline. To estimate Total Daily Energy Expenditure (TDEE), your BMR must be multiplied by a Physical Activity Level (PAL) factor or entered into our full TDEE Calculator.
Can I use pounds and inches?▼
Yes. You can toggle between Imperial (lbs, ft/in) and Metric (kg, cm) at any time. Our engine automatically normalizes inputs internally so conversion precision is maintained.
Peer-Reviewed References & Authoritative Literature
- Roza, A. M., & Shizgal, H. M. (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition, 40(1), 168–182. PMID: 6741850 • DOI: 10.1093/ajcn/40.1.168.
- Harris, J. A., & Benedict, F. G. (1918). A Biometric Study of Human Basal Metabolism. Proceedings of the National Academy of Sciences USA, 4(12), 370–373. DOI: 10.1073/pnas.4.12.370.
- Harris, J. A., & Benedict, F. G. (1919). A Biometric Study of Basal Metabolism in Man. Carnegie Institution of Washington, Publication No. 279. Washington, D.C.
- Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 105(5), 775–789. PMID: 15883556 • DOI: 10.1016/j.jada.2005.02.005.
- Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241–247. PMID: 2305711 • DOI: 10.1093/ajcn/51.2.241.
- FAO/WHO/UNU (2004). Human energy requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series 1. Rome: FAO.