Katch-McArdle Calculator – BMR from Lean Body Mass
The Katch-McArdle Calculator estimates Basal Metabolic Rate using lean body mass rather than total body weight — making it more accurate for athletes, bodybuilders, and people with above-average muscle mass or higher body fat. Enter your lean body mass and unit system to get your BMR in calories, TDEE estimates across all activity levels, and a comparison against the Mifflin-St Jeor equation result. Ideal for fitness enthusiasts who know their body composition. Formula uses the Katch-McArdle equation. For personalised dietary advice, consult a qualified doctor or dietitian.
Formula
This calculator transforms the provided inputs into the requested outputs using standard domain equations.
Quick Tip
Use this output as guidance and confirm clinical decisions with a qualified professional.
Most BMR calculators use total weight — but if you have a lot of muscle or carry significant body fat, that skews the result. The Katch-McArdle method uses lean body mass instead, giving a more accurate calorie baseline for active people.
Featured Answer
Q: How do I calculate BMR using the Katch-McArdle formula?
A: The Katch-McArdle equation calculates BMR from lean body mass: BMR = 370 + (21.6 × lean body mass in kg). For example, a person with 55 kg of lean mass has a BMR of 370 + (21.6 × 55) = 370 + 1,188 = 1,558 calories per day. This is more accurate than weight-based formulas for athletes and highly muscular individuals. Use this calculator to get your personalised result.
How to Use Katch-McArdle Calculator
- Enter your lean body mass — this is your total body weight minus fat mass. If you know your body fat percentage: lean mass = total weight × (1 − body fat %).
- Select your unit system — metric (kg) or imperial (lbs) — for the lean body mass input.
What is the Katch-McArdle BMR Formula?
The Katch-McArdle formula is a method for calculating Basal Metabolic Rate based on lean body mass (LBM) rather than total body weight. This distinction matters because muscle tissue is metabolically active — it burns more calories at rest than fat tissue. A formula that accounts for lean mass produces a more accurate BMR for anyone with above-average muscle or high body fat.
The formula: BMR = 370 + (21.6 × lean body mass in kg)
Compared to the Mifflin-St Jeor equation, which uses total weight, height, age, and sex, Katch-McArdle requires knowing lean body mass — which means you need a body composition measurement from a DEXA scan, hydrostatic weighing, bioelectrical impedance test, or a skin fold measurement.
The TDEE with activity levels output shows your Total Daily Energy Expenditure at each standard activity multiplier, giving you a complete picture of calorie needs at different exercise frequencies.
The vs Mifflin comparison shows the difference between the two methods — useful for understanding how much your body composition affects calorie estimates.
Example: Lean body mass 58 kg (from a 78 kg person at 25.6% body fat).
| Field | Value |
|---|---|
| Katch-McArdle BMR | 1,623 kcal |
| Mifflin-St Jeor BMR (est.) | 1,720 kcal |
| TDEE (Moderate, Katch) | 2,516 kcal |
| TDEE (Moderate, Mifflin) | 2,666 kcal |
At 25.6% body fat, Katch-McArdle gives a notably lower BMR — the fat tissue does not contribute to metabolic rate the way muscle does.
Katch-McArdle vs Mifflin-St Jeor: Which BMR Formula Is Right for You?
Why Katch-McArdle Calculator Matters
Most BMR calculators — including the widely used Mifflin-St Jeor — use total body weight as a key input. That works reasonably well for average-composition adults. But the moment you deviate significantly from average body fat percentage, the total-weight approach introduces meaningful error.
Consider two people who are both 80 kg at 178 cm:
- Person A is 15% body fat — largely muscle, very metabolically active.
- Person B is 35% body fat — less lean tissue, lower resting metabolic rate.
Mifflin-St Jeor gives both the same BMR. Katch-McArdle recognises that Person A's BMR is substantially higher because of greater lean mass. This distinction is not academic — it affects daily calorie targets by 200–400 calories in many cases.
If you know your body composition, Katch-McArdle is the more accurate tool. If you do not, use the BMR Calculator with the Mifflin-St Jeor formula instead.
How to Calculate BMR with the Katch-McArdle Formula — Step by Step
- Measure your body composition — use DEXA scan, hydrostatic weighing, BIA scale, or body fat percentage estimate from skin fold measurements.
- Calculate lean body mass: total weight (kg) × (1 − body fat fraction). Example: 80 kg × (1 − 0.20) = 64 kg lean mass.
- Apply the formula: BMR = 370 + (21.6 × lean body mass in kg).
- Apply activity multipliers for TDEE:
- Sedentary: BMR × 1.2
- Lightly active: BMR × 1.375
- Moderately active: BMR × 1.55
- Very active: BMR × 1.725
- Extra active: BMR × 1.9
- Compare with Mifflin-St Jeor to understand the impact of body composition on your calorie estimates.
Real-World Example
Comparing Katch-McArdle and Mifflin-St Jeor BMR across three body composition profiles for the same height and weight.
| Profile | Total Weight | Body Fat | Lean Mass | Katch BMR | Mifflin BMR | Difference |
|---|---|---|---|---|---|---|
| Athlete (male) | 80 kg | 10% | 72 kg | 1,925 kcal | 1,840 kcal | +85 kcal |
| Average (male) | 80 kg | 22% | 62.4 kg | 1,718 kcal | 1,840 kcal | −122 kcal |
| Higher fat (male) | 80 kg | 35% | 52 kg | 1,493 kcal | 1,840 kcal | −347 kcal |
For the athlete, Katch-McArdle correctly identifies a higher BMR. For the high-body-fat individual, it correctly identifies a substantially lower BMR than Mifflin assumes.
Common Mistakes to Avoid
- Using an inaccurate body fat percentage — the output is only as good as the lean mass input. Consumer BIA scales can be 3–8% off in body fat measurement. Use the most accurate body composition method available.
- Confusing total weight with lean mass — enter lean body mass, not total weight. This is the most common input error.
- Using Katch-McArdle without knowing body composition — if you do not have a measured body fat percentage, use Mifflin-St Jeor instead. Guessing body fat percentage introduces more error than using a weight-based formula.
- Applying Katch-McArdle to sedentary high-fat individuals — the formula is most accurate for people who have had their body composition measured. For sedentary average-composition adults, Mifflin-St Jeor may be more practical.
- Treating the TDEE comparison as definitive — both formulas estimate TDEE; the activity multipliers are approximations. Track actual weight changes over 2–4 weeks and adjust.
When to Use This Calculator
Use the Katch-McArdle Calculator when you have a recent body composition measurement and want the most accurate calorie baseline possible. Ideal for competitive athletes, bodybuilders, or anyone on a structured body composition programme.
For general use without body composition data, the BMR Calculator (Mifflin-St Jeor) is the more practical option. For total daily calorie planning with a goal adjustment, the Calorie Intake Calculator combines BMR with activity and goal in one step.
Pro Tips
BMR calories — this is your resting calorie floor. Any sustained eating below this level risks metabolic slowdown and muscle loss.
TDEE with activity levels — compare your result at two activity levels: your current level and one level higher. The difference shows the calorie benefit of increasing regular exercise.
Vs Mifflin comparison — if the Katch-McArdle result is notably lower than Mifflin-St Jeor, it suggests higher body fat than average. If notably higher, it suggests above-average muscle mass. Both directions are useful information.
Important Assumptions and Limitations
The Katch-McArdle formula (BMR = 370 + 21.6 × LBM kg) is validated for individuals with measured lean body mass. Accuracy depends heavily on the precision of the body composition measurement method used. Calculation reviewed against the Katch-McArdle (1975) BMR equation references. For clinical application, consult a qualified dietitian.
For personalised advice, consult a qualified doctor or dietitian.
Frequently Asked Questions
Find answers to common questions about Katch-McArdle Calculator
The Katch-McArdle formula calculates Basal Metabolic Rate from lean body mass rather than total weight: BMR = 370 + (21.6 × lean body mass in kg). It was developed to improve BMR accuracy for individuals whose body composition differs significantly from the average, such as athletes with high muscle mass or people with higher-than-average body fat percentage.
First, calculate your lean body mass: total weight × (1 − body fat fraction). Then apply the formula: BMR = 370 + (21.6 × LBM in kg). For example, 65 kg LBM gives BMR = 370 + (21.6 × 65) = 370 + 1,404 = 1,774 kcal/day. Multiply by an activity factor to get TDEE. This calculator applies the formula once you enter your lean mass.
When lean body mass is measured accurately (DEXA, hydrostatic weighing), Katch-McArdle is one of the most accurate BMR formulas available — particularly for athletes and highly muscular individuals. Accuracy decreases proportionally with the inaccuracy of the body fat measurement used to derive lean mass. Consumer BIA scales introduce more error than clinical-grade methods.
The comparison shows the difference in BMR between the Katch-McArdle formula (lean mass-based) and the Mifflin-St Jeor formula (total weight-based) for the same individual. If Katch-McArdle gives a higher BMR, the person has above-average lean mass. If it gives a lower BMR, they have above-average body fat. The gap quantifies how much body composition affects calorie estimation.
Use Katch-McArdle when you have a measured body fat percentage from a reliable source (DEXA, hydrostatic weighing, calibrated BIA). It is most valuable for athletes, bodybuilders, and body composition clients. Use Mifflin-St Jeor when body composition data is not available, as relying on an estimated body fat percentage can introduce more error than using the weight-based formula.
Using the Katch-McArdle formula: BMR = 370 + (21.6 × 60) = 370 + 1,296 = 1,666 kcal/day. At moderate activity (TDEE factor 1.55), this person burns approximately 2,582 calories per day. This is the resting plus activity baseline — actual food intake target depends on goals (maintenance, deficit, or surplus).
Yes. Calculate lean mass from your total weight and body fat percentage: lean mass = total weight × (1 − body fat %). For example, if you weigh 75 kg at 20% body fat: lean mass = 75 × 0.80 = 60 kg. Enter 60 kg as the lean body mass input. The accuracy of the result depends on how accurately your body fat percentage was measured.
Lean body mass is the metabolically active component of weight — muscle burns significantly more calories at rest than fat tissue. Two people at the same total weight can have BMRs differing by 200–400 calories if their body composition differs significantly. Katch-McArdle captures this difference; Mifflin-St Jeor does not. For high-muscle athletes, this difference meaningfully affects calorie targets.