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

Term

REE

What it means

Resting energy under standard lab protocols

Practical note

Common clinical/research term

Term

RMR

What it means

Resting metabolic rate — less strict conditions than BMR

Practical note

Often interchangeable with REE in practice

Term

BMR

What it means

Basal metabolic rate — strict fasting/rest/thermoneutral conditions

Practical note

Gold-standard terminology; often ~3–10% lower than RMR in studies

Term

TDEE

What it means

Total daily energy (resting × activity factor)

Practical note

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.

Clinical and basal-energy terminology: see our BEE Calculator. Fitness 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

Equation

Mifflin-St Jeor

Required inputs

Weight, height, age, sex

Best suited for

General adults (default auto)

Equation

Harris-Benedict (revised)

Required inputs

Weight, height, age, sex

Best suited for

Adult cross-check

Equation

Harris-Benedict (original)

Required inputs

Weight, height, age, sex

Best suited for

Historical comparison

Equation

Katch-McArdle

Required inputs

Weight + body fat %

Best suited for

Known composition

Equation

Cunningham

Required inputs

Lean body mass (kg)

Best suited for

Direct LBM / athletes

Equation

Owen

Required inputs

Weight + sex

Best suited for

Height unknown / weight-only

Equation

Schofield

Required inputs

Weight + age + sex

Best suited for

All ages / WHO bands

Dedicated deep-dives: Mifflin, Harris-Benedict, Katch-McArdle, Cunningham, Fat-Free Mass, Lean Body Mass, Owen, Schofield.

How Auto-Select Works

Your inputs

Age under 18

Auto picks

Schofield

Why

WHO age-band lifecycle estimates

Your inputs

Lean mass entered

Auto picks

Cunningham

Why

LBM-only predictor

Your inputs

Body fat % entered

Auto picks

Katch-McArdle

Why

Lean mass from weight and BF%

Your inputs

Athlete, no composition, height known

Auto picks

Mifflin-St Jeor

Why

Adult default + lean-mass guidance

Your inputs

Height not provided

Auto picks

Owen

Why

Weight-only equation

Your inputs

Default adult + height

Auto picks

Mifflin-St Jeor

Why

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.

  1. REE = (10 × 80) + (6.25 × 180) − (5 × 35) + 5
  2. 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.

  1. REE = 20.315 × 30 + 485.9
  2. REE ≈ 1,095 kcal/day

Result: Estimated REE/RMR/BMR ≈ 1,095 kcal/day

Athlete: 68 kg lean mass

Lean mass entered → Cunningham.

  1. REE = 500 + (22 × 68)
  2. REE = 1,996 kcal/day

Result: Estimated REE/RMR/BMR ≈ 1,996 kcal/day

Adult male: 80 kg, no height

Auto → Owen (weight-only).

  1. REE = 879 + (10.2 × 80)
  2. 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.

Suggested next steps

Metabolic Age Calculator

Age-equivalence from resting energy

BEE Calculator

Basal energy hub + Classic Harris-Benedict

Fat-Free Mass Calculator

Body-fat-first FFM before lean-mass TDEE

Lean Body Mass Calculator

Anthropometric LBM when BF% unknown

Calorie Surplus Calculator

Bulking presets, weekly gain & macros

RMR Calculator

RMR hub + fixed kcal goals + macros

BMR Calculator

Simpler 3-formula BMR compare

TDEE Calculator

Full daily calories + macros

Macro Calculator

Turn goal calories into macros

Maintenance Calculator

Verify maintenance from trends

Frequently Asked Questions

Common questions about the ree calculator.

What is Resting Energy Expenditure (REE)?
REE is the energy your body uses at rest for essential functions — breathing, circulation, cell repair. It is closely related to Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR), which differ mainly in how strictly they are measured in a lab.
Is REE the same as RMR or BMR?
They describe closely related concepts. BMR uses stricter measurement conditions; RMR/REE use less strict resting protocols and are often a few percent higher. This calculator shows one predictive resting-energy estimate labeled REE/RMR/BMR — not three separate numbers.
How does the REE calculator work?
Enter age, sex, weight, and usually height. Choose Auto or a specific equation. The tool estimates resting energy, shows TDEE at every activity level, goal calories, and compares all seven major predictive equations when inputs allow.
What does Auto (recommended) select?
Rules apply in priority order (first match wins): under 18 → Schofield; direct lean mass → Cunningham; body fat % → Katch-McArdle; athlete without composition (height known) → Mifflin with lean-mass guidance; no height → Owen; default adult with height → Mifflin-St Jeor.
Which equation is most accurate?
No single equation fits everyone. Frankenfield (2005) often favors Mifflin for general adults when height is known. Athletes may need lean-mass equations (O'Neill 2023). Schofield fits pediatric age bands. Compare formulas and calibrate with weight trends.
Why do different calculators give different REE?
Different equations, activity multipliers, and labels (BMR vs REE) change results. Even the same equation can differ if height, age, or body composition inputs differ. Use 2–3 weeks of weight trends to judge which estimate fits you.
What is indirect calorimetry?
The gold-standard lab method measuring oxygen consumption and carbon dioxide production to calculate resting energy expenditure directly. Predictive equations are practical estimates — not replacements for measurement.
Can athletes rely on predictive REE equations?
With caution. O'Neill et al. (2023) found several common equations, including Mifflin and Owen, differed significantly from measured RMR in pooled athlete data. Lean-mass equations may fit better when body composition is known.
Can children use this REE calculator?
Auto-select uses Schofield for users under 18. Pediatric meal planning requires professional guidance — this tool is educational only, not clinical prescribing.
Does REE equal TDEE?
No. TDEE = resting energy × activity factor (plus thermic effect of food is approximated in the multiplier). REE/RMR/BMR is only the resting component — multiply by activity before planning deficits or surpluses.
What activity multipliers does this use?
Fitness-oriented multipliers from 1.2 (sedentary) to 1.9 (extra active). WHO/clinical PAL categories used in hospitals differ — see our methodology page.
What goal options are available?
Maintain, mild/moderate/larger deficit (−10/−15/−20%), and lean gain (+5%) or weight gain (+10%) surpluses applied to TDEE.
Why show a ±10% range?
Population equations commonly miss measured resting energy by roughly 10–15%. The range sets realistic expectations before you calibrate with real weight data.
What protein does the calculator suggest?
For ages 18+, a g/kg range on total body weight based on your goal. Do not use adult protein targets for minors.
How often should I recalculate REE?
When weight, age band, body composition, or training volume changes meaningfully — often every few weeks during active dieting or growth phases.
Is this medical or clinical advice?
No. Informational tool for personal awareness and nutrition journaling only — not for prescribing hospital, ICU, or enteral feeds.
How is this different from the BMR Calculator?
The BMR Calculator compares three formulas (Mifflin, Harris, Katch) without TDEE goals. This REE hub adds auto-select, all seven equations, TDEE tables, and goal calories.
Does this store my data?
Inputs may persist in browser local storage for convenience. Calculations run locally; nothing is sent to a server.
Can I compare all formulas at once?
Yes — the results panel shows a comparison table for Mifflin, Harris (original and revised), Katch, Cunningham, Owen, and Schofield when your inputs support each equation.
Why is height optional?
Owen and Schofield do not require height in their core math. Auto-select uses Owen when height is omitted for adults; Mifflin and Harris need height and appear unavailable in the comparison table until height is entered.
What body fat or lean mass should I enter?
Only if you have a reliable estimate (DEXA, BIA, skilled caliper, Navy method on dedicated tools). Guessed body fat reduces accuracy for Katch and Cunningham.
Where do the equations come from?
Peer-reviewed sources: Mifflin (1990), Harris-Benedict (1919/1984), Katch-McArdle (exercise physiology texts), Cunningham (1980), Owen (1986/1987), Schofield/WHO (1985). See the references section on this page.

Research & References

Each citation below supports a specific claim on this page. We explain relevance so you can verify the science yourself.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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).
  9. 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.
  10. 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.
  11. 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.