Katch-McArdle BMR Calculator
Calculate BMR using the Katch-McArdle formula, which accounts for lean body mass.
How to use this tool
- Enter lean body mass in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your bmr and the full breakdown beneath it.
The Katch-McArdle formula uses lean body mass (LBM) instead of total weight, making it more accurate for lean or muscular individuals.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
BMR (kcal/day) = 370 + 21.6 × lean body mass (kg)
How it works
The Katch-McArdle formula calculates basal metabolic rate from lean body mass (LBM) rather than total body weight, making it more accurate than weight-based formulae for people with above-average or below-average body fat percentages. The constant 370 represents the baseline metabolic expenditure independent of lean tissue, while 21.6 kcal per kilogram of LBM per day approximates the energy cost of maintaining metabolically active tissue. LBM must be known or separately estimated (e.g. from body fat percentage measurements) before using this calculator.
Worked example
- Lean body mass = 56 kg.
- Apply the formula: BMR = 370 + 21.6 × 56.
- 21.6 × 56 = 1209.6.
- BMR = 370 + 1209.6 = 1579.6 kcal/day.
BMR = 1579.6 kcal/day
Common mistakes to avoid
- Entering total body weight instead of lean body mass — the Katch-McArdle formula specifically uses LBM (kg), not gross weight, which is what distinguishes it from Harris-Benedict.
- Estimating lean body mass from body fat percentage without measuring body fat accurately — a rough guess of body fat % leads to an equally rough LBM and BMR.
- Using the resulting BMR as a calorie target for weight loss without multiplying by an activity factor to get TDEE first.
Key terms
- BMR (Basal Metabolic Rate)
- The minimum number of calories the body needs at complete rest to maintain basic physiological functions such as breathing, circulation, and cell repair.
- Lean body mass (LBM)
- Total body weight minus fat mass, comprising muscle, bone, water, and organs; the metabolically dominant component of body composition.
- Katch-McArdle formula
- A BMR equation developed in the 1970s that uses lean body mass instead of total weight, providing better accuracy across a wider range of body compositions.
- Body fat percentage
- The proportion of total body weight attributable to fat; used alongside total weight to calculate lean body mass for this formula.
- TDEE (Total Daily Energy Expenditure)
- BMR multiplied by an activity factor to estimate total daily calorie needs; the first step in designing a diet or nutrition plan.
Frequently asked questions
- What makes Katch-McArdle different from Mifflin-St Jeor?
- Katch-McArdle uses lean body mass rather than total body weight, so it is more accurate for people who know their body fat percentage. Mifflin-St Jeor only needs weight, height, age, and sex.
- How do I find my lean body mass?
- Subtract fat mass from total weight. Use our Lean Body Mass Calculator to estimate LBM from height, weight and sex using the Boer formula.