What Is Resting Energy Expenditure (REE)?
Resting Energy Expenditure (REE) is the energy your body uses at rest to maintain essential functions — breathing, circulation, organ work, and cell repair. In research and clinical nutrition, REE is often measured by indirect calorimetry (gas exchange). In everyday practice, validated predictive equations estimate REE from body size, age, sex, and sometimes body composition when lab measurement is unavailable.
REE vs RMR vs BMR vs TDEE
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| Term | What it means | Practical note |
|---|---|---|
| REE | Resting energy under standard lab protocols | Common clinical/research term |
| RMR | Resting metabolic rate — less strict conditions than BMR | Often interchangeable with REE in practice |
| BMR | Basal metabolic rate — strict fasting/rest/thermoneutral conditions | Gold-standard terminology; often ~3–10% lower than RMR in studies |
| TDEE | Total daily energy (resting × activity factor) | Maintenance and goal calorie planning |
This calculator shows one predictive resting-energy estimate labeled REE / RMR / BMR — not three separate numbers. Predictive equations cannot distinguish measurement protocol; they provide a practical resting kcal/day starting point.
Fitness and weight-management framing: see our RMR Calculator for the same seven equations with RMR-first terminology, fixed kcal targets, and macro preview.
How REE Is Measured vs Predicted
Indirect calorimetry measures oxygen consumption and carbon dioxide production to calculate energy expenditure — the reference method in hospitals and research. Predictive equations (Mifflin, Harris, Katch, Cunningham, Owen, Schofield) estimate REE from anthropometrics and are faster and cheaper, but individual error commonly reaches roughly ±10–15%.
TDEE estimate error comes from two stacked layers — and the second is usually bigger in practice.
Layer 1: BMR formula error
Mifflin-St Jeor predicts resting metabolic rate within ~10% for roughly 82% of non-obese adults and ~70% of obese adults (Frankenfield et al., 2005). That is ±150–200 kcal for many people.
Layer 2: Activity multiplier error
Picking one activity bucket too high adds ~200–400 kcal/day. Most people remember gym time but underestimate desk hours. Take our Activity Level Quiz if unsure.
Seven Predictive Equations Compared
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| Equation | Required inputs | Best suited for |
|---|---|---|
| Mifflin-St Jeor | Weight, height, age, sex | General adults (default auto) |
| Harris-Benedict (revised) | Weight, height, age, sex | Adult cross-check |
| Harris-Benedict (original) | Weight, height, age, sex | Historical comparison |
| Katch-McArdle | Weight + body fat % | Known composition |
| Cunningham | Lean body mass (kg) | Direct LBM / athletes |
| Owen | Weight + sex | Height unknown / weight-only |
| Schofield | Weight + age + sex | All ages / WHO bands |
Dedicated deep-dives: Mifflin, Harris-Benedict, Katch-McArdle, Cunningham, Owen, Schofield.
How Auto-Select Works
Your inputs
Auto picks
Why
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| Your inputs | Auto picks | Why |
|---|---|---|
| Age under 18 | Schofield | WHO age-band lifecycle estimates |
| Lean mass entered | Cunningham | LBM-only predictor |
| Body fat % entered | Katch-McArdle | Lean mass from weight and BF% |
| Athlete, no composition, height known | Mifflin-St Jeor | Adult default + lean-mass guidance |
| Height not provided | Owen | Weight-only equation |
| Default adult + height | Mifflin-St Jeor | Frankenfield 2005 general adult preference |
Official Formulas (Reference)
Mifflin-St Jeor
Male:
BMR = (10 × kg) + (6.25 × cm)
− (5 × age) + 5
Female:
BMR = (10 × kg) + (6.25 × cm)
− (5 × age) − 161- kg
- Body weight in kilograms
- cm
- Height in centimeters
- age
- Age in years
Schofield (WHO age bands)
BMR/REE (kcal/day) = a × weight (kg) + b Coefficients (a, b) depend on sex and age band: Under 3 · 3–10 · 10–18 · 18–30 · 30–60 · 60+ years Source: Schofield (1985); FAO/WHO Table 5.2 (weight-only).
- kg, age, sex
- Weight-only kcal/day by age band
Katch-McArdle
Lean mass (kg) = weight (kg)
× (1 − body fat % / 100)
BMR = 370 + (21.6 × lean mass kg)- kg
- Body weight in kilograms
- BF%
- Body fat percentage (required)
Cunningham (1980)
RMR = 500 + (22 × lean mass kg) Lean mass can be entered directly, or: lean mass = weight (kg) × (1 − body fat % / 100)
- kg
- Lean body mass in kilograms
Worked Examples
Adult male: 35 y, 180 cm, 80 kg
Auto → Mifflin-St Jeor.
- REE = (10 × 80) + (6.25 × 180) − (5 × 35) + 5
- REE ≈ 1,755 kcal/day
Result: Estimated REE/RMR/BMR ≈ 1,755 kcal/day
Child: female, 8 y, 130 cm, 30 kg
Auto → Schofield 3–10 band.
- REE = 20.315 × 30 + 485.9
- REE ≈ 1,095 kcal/day
Result: Estimated REE/RMR/BMR ≈ 1,095 kcal/day
Athlete: 68 kg lean mass
Lean mass entered → Cunningham.
- REE = 500 + (22 × 68)
- REE = 1,996 kcal/day
Result: Estimated REE/RMR/BMR ≈ 1,996 kcal/day
Adult male: 80 kg, no height
Auto → Owen (weight-only).
- REE = 879 + (10.2 × 80)
- REE = 1,695 kcal/day
Result: Estimated REE/RMR/BMR ≈ 1,695 kcal/day
Factors Affecting REE
Resting energy varies with body size, lean mass, age, sex, genetics, hormones, sleep, stress, illness, medications, and environment. Predictive equations capture population averages — not your measured metabolism. Body composition often explains why two people of the same weight can differ in resting energy.
Athletes & Body Composition
O'Neill et al. (2023) found common equations including Mifflin and Owen differed significantly from measured RMR in pooled athlete data. When lean mass or body fat is known, Cunningham or Katch-McArdle may provide useful comparisons — but no equation replaces individual calibration or indirect calorimetry for precision work.
Clinical Context (Informational Only)
REE estimates inform hospital nutrition, ICU planning, obesity treatment, and research — but this calculator is for personal awareness and education only. Clinical teams use measured REE, disease-specific factors, and professional judgment — not a web calculator alone.
Common Mistakes
- Confusing REE with TDEE — multiply by activity before planning deficits or surpluses.
- Expecting three different resting numbers — BMR, RMR, and REE are terminology for measurement context, not three outputs here.
- Guessing body fat % — Katch and Cunningham depend on composition quality.
- Using outdated weight — recalculate when weight changes meaningfully.
Myths vs Facts
Myth
One equation is always most accurate.
Evidence-based view
Accuracy depends on population and inputs. Mifflin suits many general adults; Schofield spans ages; lean-mass equations suit composition-aware users.
Myth
REE and TDEE are the same.
Evidence-based view
REE is resting only. TDEE adds activity (and approximates thermic effect of food in the multiplier).
Myth
Online calculators replace indirect calorimetry.
Evidence-based view
Indirect calorimetry remains the measurement gold standard. Equations are starting estimates.
Myth
Athletes should always use Mifflin.
Evidence-based view
Athlete cohorts vary. Compare lean-mass equations when composition is known; validate with trends.
Frequently Asked Questions
Common questions about the ree calculator.
Research & References
Each citation below supports a specific claim on this page. We explain relevance so you can verify the science yourself.
- National Academies of Sciences, Engineering, and Medicine — Factors Affecting Energy Expenditure and Requirements. Dietary Reference Intakes for Energy — NCBI Bookshelf, 2023.Defines TDEE components (REE, TEF, PAEE) and explains why population equations cannot capture individual metabolic variation.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247, 1990.Primary source for the Mifflin-St Jeor BMR equation used as the default in this calculator.
- 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, 1984.Source for the revised Harris-Benedict coefficients — default equation on this calculator page.
- McArdle WD, Katch FI, Katch VL — Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins, 7th edition, 2010.Textbook reference for the lean-body-mass-based Katch-McArdle resting energy estimate.
- Frankenfield D, Roth-Yousey L, Compher C — Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. J Am Diet Assoc. 2005;105(5):775-789, 2005.Meta-analysis showing Mifflin-St Jeor within ~10% of measured RMR for ~82% of non-obese and ~70% of obese adults — supports honest accuracy framing.
- O'Neill JER, Corish CA, Horner K — Accuracy of Resting Metabolic Rate Prediction Equations in Athletes: A Systematic Review with Meta-analysis. Sports Med. 2023;53(12):2373-2398, 2023.Athlete systematic review and meta-analysis — several common equations including Mifflin-St Jeor and Owen differed significantly from measured RMR in pooled athlete data; lean-mass equations (e.g., Cunningham 1980) and Ten-Haaf performed differently by population, with no single best equation for all athletes.
- Cunningham JJ — A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr. 1980;33(11):2372-2374, 1980.Primary source for the Cunningham equation (500 + 22 × lean body mass kg). Cunningham’s paper labels the output BMR; the 1980 reanalysis of Harris-Benedict (1919) data found LBM as the single predictor, with sex and age adding little once LBM was included.
- Schofield WN — Predicting basal metabolic rate, new standards and review of previous work. Hum Nutr Clin Nutr. 1985;39 Suppl 1:5-41, 1985.Primary source for the Schofield age- and sex-specific BMR predictive equations (weight-only kcal/day form retained in FAO/WHO Table 5.2).
- FAO/WHO/UNU — Human Energy Requirements — Report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series, 2001.Table 5.2 Schofield (1985) kcal/day coefficients by age and sex; documents retention of these equations and notes on geographic/ethnic applicability limits.
- Owen OE, Kavle EC, Owen RS, Polansky M, Caprio S, Mozzoli MA, Kendrick ZV, Bushman MC, Boden G — A reappraisal of caloric requirements in healthy women. Am J Clin Nutr. 1986;44(1):1-19, 1986.Primary source for Owen female RMR equations — non-athlete (795 + 7.18 × weight kg) and athlete (50.4 + 21.1 × weight kg) variants.
- Owen OE, Holup JL, D'Alessio DA, Craig ES, Polansky M, Smalley KJ, Kavle EC, Bushman MC, Owen LR, Mozzoli MA, Kendrick ZV, Boden G — A reappraisal of the caloric requirements of men. Am J Clin Nutr. 1987;46(6):875-885, 1987.Primary source for Owen male RMR equation (879 + 10.2 × weight kg) in men 18–82 years; found weight alone predicted RMR with age effect trivial.