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. When body fat % is known, start with the Fat-Free Mass Calculator; use the Lean Body Mass Calculator when you only have height and weight.

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.

  1. LBM = 80 × (1 − 0.15) = 68 kg
  2. 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.

  1. LBM = 62 × 0.78 = 48.36 kg
  2. BMR = 370 + (21.6 × 48.36) ≈ 1,415 kcal/day

Result: Estimated BMR ≈ 1,415 kcal/day

How This Calculator Works

Step

1. Body fat

What you enter

Manual %, lab value, or US Navy estimate

Result

Body fat % used for LBM

Step

2. Lean mass

What you enter

Weight + body fat %

Result

LBM and fat mass (kg)

Step

3. BMR

What you enter

Katch-McArdle formula

Result

Resting calories + ±10% range

Step

4. TDEE & goals

What you enter

Activity multiplier + goal

Result

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

Mifflin-St Jeor

Required inputs

Weight, height, age, sex

Often best when

General adults; default when BF% unknown

Formula

Harris-Benedict (1984)

Required inputs

Weight, height, age, sex

Often best when

Legacy comparison; similar use case to Mifflin

Formula

Katch-McArdle

Required inputs

Weight + body fat %

Often best when

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.

Suggested next steps

U.S. Navy Body Fat Calculator

Dedicated circumference BF% hub

Fat-Free Mass Calculator

FFM from DEXA, BIA, Navy & manual BF%

Lean Body Mass Calculator

Boer, James, Hume when BF% unknown

RMR Calculator

RMR hub with fixed kcal goals

REE Calculator

All 7 equations + auto-select + TDEE

BMR Calculator

Compare Mifflin, Harris-Benedict, and Katch side by side

Macro Calculator

Turn goal calories into protein, fat, and carbs

Calorie Surplus Calculator

Bulking presets from lean-mass TDEE

Maintenance Calculator

Verify maintenance from real-world weight data

Methodology

How we frame accuracy and calibration on tdee.fitliferegime.com

Frequently Asked Questions

Common questions about the katch-mcardle calculator.

What is the Katch-McArdle equation?
A lean-body-mass-based formula: BMR = 370 + (21.6 × lean mass kg), where lean mass = weight × (1 − body fat % / 100). It estimates resting energy from metabolically active tissue rather than total weight.
What is the Katch-McArdle formula?
First calculate LBM: weight (kg) × (1 − BF%/100). Then BMR = 370 + 21.6 × LBM. No height or age is required for the core equation.
When should I use Katch-McArdle instead of Mifflin-St Jeor?
When you have a reliable body fat % estimate — often for leaner or athletic individuals. If body fat is unknown or from an unreliable scale, Mifflin is usually the better default.
Is Katch-McArdle more accurate than Mifflin?
Not automatically. It depends on body fat measurement quality. A 2023 athlete meta-analysis (O'Neill et al.) found equation performance varied by population — Mifflin-St Jeor significantly underestimated RMR in some athlete cohorts, while lean-mass equations such as Cunningham (1980) performed differently by sport and sex. For general adults with uncertain BF%, Mifflin is usually the safer default.
What body fat % do I need?
Enter a value between 3% and 70%. Use lab/DEXA when available, skilled calipers consistently, or the US Navy estimator built into this calculator as a rough field method.
How does the US Navy body fat option work?
It applies the U.S. Navy circumference method (neck, waist, and hip for women; height required) to estimate body fat %, then feeds that value into Katch-McArdle. Men measure waist at the navel; women at the narrowest point. It is a field estimate — less precise than DEXA or skilled calipers.
What is lean body mass (LBM)?
In this tool, LBM = total weight minus fat mass, estimated from body fat %. It represents the non-fat component of your body weight used in the formula.
How is Katch-McArdle different from Cunningham?
Both use lean mass. Cunningham (1980) uses BMR = 500 + 22×LBM; Katch-McArdle uses 370 + 21.6×LBM. They are related but not identical — compare both in results.
Do I need height and age?
Not for Katch-McArdle itself — only weight and body fat %. Optional age, sex, and height enable Mifflin/Harris cross-checks and BMI context.
How do I get TDEE from Katch-McArdle BMR?
Multiply BMR by an activity factor (1.2–1.9). This calculator shows TDEE at every activity level and applies your selected multiplier.
What activity multiplier should I use?
Start with the Activity Level Quiz or pick the description closest to your typical week. When in doubt, choose the lower multiplier and adjust from weight trends.
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, same as other BMR tools on this site.
Why show a ±10% BMR range?
Population equations commonly miss individual measured RMR by roughly 10–15%. The range sets realistic expectations before you calibrate with real weight data.
Can I compare with Harris-Benedict?
Yes — add optional age, sex, and height to see Mifflin-St Jeor and Harris-Benedict (revised) BMR estimates alongside Katch-McArdle.
Does higher body fat mean lower BMR with Katch?
At the same total weight, yes — more fat mass means less lean mass, which lowers the Katch estimate. That matches the idea that fat tissue is less metabolically active than lean tissue.
Is this good for bodybuilders?
It can be useful when body fat is tracked consistently (e.g., contest prep), but verify against weight trends. Do not treat any equation as a substitute for measured intake response.
What protein does the calculator suggest?
A g/kg range based on total body weight and your selected goal (maintain, fat loss, or muscle gain), aligned with ISSN-style sports-nutrition summaries — not lean mass. Use the macro calculator for a full protein/fat/carb split.
How often should I recalculate?
When weight or body composition changes meaningfully — often every few weeks during active fat loss or muscle gain, or after a new DEXA/caliper assessment.
Can I use smart-scale body fat?
You can, but home BIA varies with hydration and food timing. Use trends over single readings and prefer lab methods when precision matters.
Does this store my data?
Inputs may persist in your browser local storage for convenience. Calculations run locally; nothing is sent to a server.
Is this medical advice?
No. Informational tool for personal awareness and nutrition journaling only.
Where does Katch-McArdle come from?
The form BMR = 370 + (21.6 × lean mass kg) is widely cited in exercise physiology literature (McArdle, Katch & Katch) and nutrition software. It belongs to the lean-mass RMR equation family alongside Cunningham (1980), which uses different constants (500 + 22×LBM).

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. 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.
  7. 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.
  8. 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.
  9. Hodgdon JA, Beckett MB — Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center Technical Report 84-11, 1984; companion report 84-29 for women, 1984.IOM/NAP summary documents the Hodgdon & Beckett (1984) U.S. Navy circumference body-fat equations (NHRC reports 84-11 and 84-29) used when Navy body fat % is selected in this calculator.