What Is the Katch-McArdle Equation?
The Katch-McArdle formula estimates resting metabolic rate (RMR/BMR) from lean body mass (LBM) rather than total weight, height, age, and sex. It appears widely in exercise physiology texts (McArdle, Katch & Katch) and nutrition software as an option when body composition is known. Because metabolically active tissue drives resting energy more than stored fat, LBM-based equations can align better with measured RMR in some lean or athletic groups — but only when body fat percentage is measured accurately.
Lean Mass vs Fat-Free Mass
In everyday nutrition tools, lean body mass usually means total weight minus fat mass. Strict lab definitions of fat-free mass (FFM) can include bone, water, and organ tissue slightly differently. Katch-McArdle uses the practical estimate: LBM = weight × (1 − body fat % / 100). Small definitional differences rarely change your calorie planning as much as measurement error in body fat % itself.
The Katch-McArdle Formula
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) — related, not identical
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
Cunningham uses 500 + 22×LBM; Katch-McArdle uses 370 + 21.6×LBM. They are often grouped as “LBM equations” but produce different numbers — compare both in the calculator and calibrate with real-world weight trends. For direct lean-mass entry (DEXA/BIA reports), use the Cunningham RMR Calculator.
Worked Examples
Lean male: 80 kg at 15% body fat
Common gym-goer with DEXA or reliable caliper estimate.
- LBM = 80 × (1 − 0.15) = 68 kg
- BMR = 370 + (21.6 × 68) = 370 + 1,468.8 ≈ 1,839 kcal/day
Result: Estimated BMR ≈ 1,839 kcal/day
Female athlete: 62 kg at 22% body fat
Moderate body fat with regular training.
- LBM = 62 × 0.78 = 48.36 kg
- BMR = 370 + (21.6 × 48.36) ≈ 1,415 kcal/day
Result: Estimated BMR ≈ 1,415 kcal/day
How This Calculator Works
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| Step | What you enter | Result |
|---|---|---|
| 1. Body fat | Manual %, lab value, or US Navy estimate | Body fat % used for LBM |
| 2. Lean mass | Weight + body fat % | LBM and fat mass (kg) |
| 3. BMR | Katch-McArdle formula | Resting calories + ±10% range |
| 4. TDEE & goals | Activity multiplier + goal | Maintenance and target calories |
Body Fat Accuracy Matters Most
Katch-McArdle is only as good as your body fat input. Consumer scales, handheld BIA devices, and circumference methods can drift by several percentage points. DEXA, hydrostatic weighing, or skilled multi-site calipers (when done consistently) tend to be more reliable — but still carry error. If you are unsure of body fat %, Mifflin-St Jeor is usually the safer default for general adults.
Katch-McArdle vs Mifflin-St Jeor vs Harris-Benedict
Mifflin-St Jeor (1990) — general default
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
Formula
Required inputs
Often best when
Formula
Required inputs
Often best when
Formula
Required inputs
Often best when
| Formula | Required inputs | Often best when |
|---|---|---|
| Mifflin-St Jeor | Weight, height, age, sex | General adults; default when BF% unknown |
| Harris-Benedict (1984) | Weight, height, age, sex | Legacy comparison; similar use case to Mifflin |
| Katch-McArdle | Weight + body fat % | Lean/athletic when BF% measured well |
A 2023 athlete systematic review and meta-analysis (O'Neill et al., Sports Medicine) compared many RMR prediction equations. Cunningham (1980) — which uses the same lean-mass logic as Katch-McArdle but different constants — was among equations without significant mean bias versus measured RMR in some pooled athlete analyses, while Mifflin-St Jeor significantly underestimated RMR in several athlete subgroups. Performance varied by sex, sport, and measurement protocol; no single equation was best for all athletes.
Who Should Use Katch-McArdle?
Consider Katch-McArdle when you have a recent, trustworthy body fat estimate and your physique is leaner or more muscular than population-average. Strength athletes, physique competitors, and regular lifters with DEXA or consistent caliper tracking are common use cases. If you carry higher body fat or only have a bathroom-scale BIA reading, start with Mifflin-St Jeor and validate with weight trends.
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.
Common Mistakes
- Treating Katch as automatically “most accurate” — accuracy depends on body fat measurement quality. A poor BF% estimate can yield less accurate results than Mifflin-St Jeor.
- Using BMR as daily calories — multiply by activity for TDEE; plan from maintenance or goal calories.
- Confusing Cunningham with Katch-McArdle — both use lean mass but different constants (500+22×LBM vs 370+21.6×LBM).
- Never recalibrating — re-estimate as weight or composition changes; verify with 2–3 weeks of scale trends.
Myths vs Facts
Myth
Katch-McArdle is always better than Mifflin.
Evidence-based view
Meta-analyses in general populations often favor Mifflin when body fat is unknown. Katch can help when BF% is measured well.
Myth
You need height and age for Katch-McArdle.
Evidence-based view
The core formula only needs weight and body fat %. Height and age enable cross-checks and BMI context in this tool.
Myth
Smart-scale body fat is lab-grade.
Evidence-based view
Home BIA can shift with hydration and food intake. Treat as a trend, not absolute truth.
Myth
LBM equations work equally for all athletes.
Evidence-based view
Sport, sex, and measurement protocol affect equation performance. Use trends to verify.
Frequently Asked Questions
Common questions about the katch-mcardle 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.
- Jager R, Kerksick CM, Campbell BI, et al. — International Society of Sports Nutrition Position Stand: Protein and Exercise. J Int Soc Sports Nutr. 2017;14:20, 2017.Supports 1.6–2.2 g/kg/day protein ranges for many exercising adults — basis for protein and macro guidance.
- 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 comparing RMR prediction equations — supports framing that lean-mass equations (e.g., Cunningham 1980) and Mifflin-St Jeor perform 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.