BMR Calculator — Katch-McArdle Formula
The Katch-McArdle formula calculates BMR directly from lean body mass, bypassing the inaccuracy that sex, age, and total weight introduce for very lean or muscular people. Enter your weight, body fat %, and activity level.
kg
%
Activity level
Katch-McArdle formula — based on lean body mass
20%
body fatLean mass
80%
Fat mass
20%
- 1
Fat mass
80 × (20 ÷ 100) = 16 - 2
Lean body mass (LBM)
80 − 16 = 64 - 3
BMR (Katch-McArdle)
370 + 21.6 × 64 = 1,752Only lean tissue drives resting metabolism — fat mass contributes almost nothing.
How does this calculator work?
Katch-McArdle BMR = 370 + (21.6 × lean body mass in kg), where lean body mass = weight × (1 − body fat% / 100). Unlike formulas that use total weight, this equation responds directly to your muscle-to-fat ratio, making it the most accurate BMR formula for athletes. Multiply BMR by an activity factor (1.2–1.9) to get TDEE.
Formula
How this is calculated
Most BMR equations (Mifflin-St Jeor, Harris-Benedict) use total body weight, height, age, and sex as proxies for lean body mass — the metabolically active tissue that actually drives resting energy expenditure. The Katch-McArdle formula, published in 1996, cuts straight to the source: it takes lean body mass (LBM) in kilograms as its only body-composition input. The formula is BMR = 370 + (21.6 × LBM), where LBM is derived from total weight and body fat percentage: LBM = weight × (1 − body fat% / 100).
Because fat tissue has very low metabolic activity compared to muscle and organs, the Katch-McArdle formula produces more accurate BMR estimates for athletes, bodybuilders, and anyone with an unusual muscle-to-fat ratio. Two people with the same total weight but different body compositions will get different results, whereas the Mifflin and Harris-Benedict equations would give them the same BMR. The trade-off is that you need a reliable body fat percentage measurement — a value from DEXA scanning, hydrostatic weighing, or a calibrated bioelectrical impedance device gives the best accuracy; the pinch-test and online estimators introduce uncertainty.
TDEE is then estimated by multiplying BMR by a physical activity factor ranging from 1.2 (sedentary) to 1.9 (very active). As with all BMR formulas, the output is a population-average estimate — individual metabolic rates vary by 10–15% even when body composition is measured precisely.
Frequently asked questions
Standard BMR equations use total weight and height as imperfect proxies for lean mass. For athletes who carry far more muscle than average, those formulas underestimate BMR. Katch-McArdle uses lean body mass directly, so it correctly assigns a higher metabolic rate to the same total weight if muscle mass is higher.
DEXA scanning is considered the gold standard (usually available at sports clinics or hospitals). Hydrostatic weighing and air-displacement plethysmography (Bod Pod) are also highly accurate. Bioelectrical impedance analysis (BIA) scales and handheld devices are convenient but variable. Skin-fold caliper methods, done by a trained technician, are reasonably accurate. Online estimators from photos or measurements should be treated as rough approximations only.
For people with average body composition, Katch-McArdle and Mifflin-St Jeor give similar results — often within 50–100 kcal/day. For lean athletes or people with high body fat, the difference can be larger. Katch-McArdle is preferred when a reliable body fat measurement is available; Mifflin-St Jeor is the default when it is not.
Also known as
TG we-Calculate Editorial Team. (2026). BMR Calculator — Katch-McArdle Formula [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/bmr-katch-mcardle-calculator
TG we-Calculate Editorial Team. "BMR Calculator — Katch-McArdle Formula." TG we-Calculate. 2026. https://we-calculate.com/calculator/bmr-katch-mcardle-calculator.
TG we-Calculate Editorial Team, "BMR Calculator — Katch-McArdle Formula," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/bmr-katch-mcardle-calculator
@misc{wecalculate_bmr_katch_mcardle_calculator, title = {BMR Calculator — Katch-McArdle Formula}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/bmr-katch-mcardle-calculator}}, year = {2026}, note = {TG we-Calculate} }
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