SCIENTIFIC METHODOLOGY
BMR Formulas & Equations.
Explore the exact clinical mathematics behind our calculator. We compare Mifflin–St Jeor, the 1984 Revised Harris–Benedict, and Katch–McArdle equations with their original peer-reviewed sources.
Formula Comparison Matrix
Different formulas were derived on distinct historical cohorts and serve specific athletic or demographic profiles:
| Formula | Year | Required Inputs | Best Suited For | Clinical Accuracy |
|---|---|---|---|---|
| Mifflin–St Jeor | 1990 | Weight (kg), Height (cm), Age, Sex | General public, both non-obese and obese adults | Highest (gold-standard in clinical dietetics) |
| Revised Harris–Benedict | 1984 | Weight (kg), Height (cm), Age, Sex | Historical reference, active individuals | Moderate (tends to overestimate by ~5%) |
| Katch–McArdle | 1977 | Weight (kg), Body Fat % | Athletes, bodybuilders, individuals with known body fat | High for lean physiques (sex-neutral) |
1. The Mifflin–St Jeor Equation (1990)
Introduced by Dr. Mark D. Mifflin and S. T. St Jeor in 1990, this equation is considered the clinical gold standard by the Academy of Nutrition and Dietetics. It was formulated on 498 healthy subjects across normal and obese weight categories.
Variables: W = Weight in kg, H = Height in cm, A = Age in years
Male: BMR = (10 × W) + (6.25 × H) - (5 × A) + 5Female: BMR = (10 × W) + (6.25 × H) - (5 × A) - 161Citation: Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.PubMed ↗
2. The Revised Harris–Benedict Equation (1984)
The original 1919 Harris-Benedict formula was one of the earliest mathematical models of human metabolism. In 1984, researchers Roza and Shizgal re-analyzed extensive human calorimeter data to eliminate known overestimation errors.
Variables: W = Weight in kg, H = Height in cm, A = Age in years
Male: BMR = 88.362 + (13.397 × W) + (4.799 × H) - (5.677 × A)Female: BMR = 447.593 + (9.247 × W) + (3.098 × H) - (4.330 × A)Citation: Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182.PMC Article ↗
3. The Katch–McArdle Equation
Unlike Mifflin–St Jeor and Harris–Benedict, Katch–McArdle does not take age, height, or biological sex into account. Instead, it predicts basal calorie burn strictly from Lean Body Mass (LBM). Because muscle tissue is the primary metabolic engine of the body, two individuals with identical lean mass will have nearly identical baseline energy needs regardless of age or gender.
Lean Body Mass (LBM) in kg = Total Weight (kg) × (1 - Body Fat % / 100)BMR = 370 + (21.6 × LBM in kg)Note: This equation requires a reasonably accurate body fat percentage (e.g. from DEXA scan, hydrostatic weighing, or skinfold calipers).
Activity Multipliers (TDEE Physical Activity Ratios)
To convert resting BMR to Total Daily Energy Expenditure (TDEE), your BMR is multiplied by an activity factor derived from the World Health Organization (WHO) and Institute of Medicine (IOM) standards:
- Sedentary (1.200x): Little to no physical exercise; desk job, minimal movement.
- Lightly Active (1.375x): Light training or walking 1 to 3 days per week.
- Moderately Active (1.550x): Moderate exercise or sport 3 to 5 days per week.
- Very Active (1.725x): Intense training or strenuous sports 6 to 7 days per week.
- Extremely Active (1.900x): Heavy physical labor or athletic two-a-day training regimens.