Most BMR calculators rely solely on total body weight, which fails to distinguish between metabolically active muscle and relatively inert fat tissue. The Katch-McArdle Calculator takes a different approach: it calculates your Basal Metabolic Rate directly from your lean body mass, the weight of everything in your body that is not fat. This makes it one of the most physiologically sound equations available, especially for individuals who are muscular, athletic, or have body compositions that fall outside population averages. Whether you have your LBM from a DEXA scan, know your body fat percentage from calipers or a smart scale, or need the tool to estimate your LBM from your weight, height, and sex using the Boer formula, Toolraxy provides a free, client-side calculator that puts body-composition-aware metabolic estimation in your hands.
How to Use the Katch-McArdle Calculator
Select your LBM input mode from the dropdown at the top: “I don’t know my LBM,” “I know my LBM,” or “I know my body fat %.”
If estimating LBM, select your sex and enter your weight and height. The tool uses the Boer formula to estimate LBM.
If you know your LBM, enter it directly and select kilograms or pounds.
If you know your body fat percentage, enter your weight and body fat percentage. LBM is calculated as Weight × (1 – Body Fat% ÷ 100).
The Katch-McArdle equation display updates with your numbers. Click Calculate. The tool displays your LBM, BMR, and maintenance calories at four activity levels: sedentary, light, moderate, and very active.
How the Tool Works
This Katch-McArdle Calculator determines lean body mass through one of three methods, then applies the Katch-McArdle BMR equation.
Lean Body Mass Determination:
Method 1: Estimated from weight, height, and sex using the Boer formula.
For males: LBM (kg) = (0.407 × weight in kg) + (0.267 × height in cm) – 19.2
For females: LBM (kg) = (0.252 × weight in kg) + (0.473 × height in cm) – 48.3
Method 2: User enters LBM directly. Pounds are converted to kilograms (× 0.453592).
Method 3: User enters weight and body fat percentage.
LBM (kg) = Weight in kg × (1 – Body Fat% ÷ 100)
BMR Calculation (Katch-McArdle Equation):
BMR = 370 + (21.6 × LBM in kg)
The result is rounded to the nearest whole number. This equation is notable because it does not include age, sex, or height as variables—only lean body mass matters. This reflects the physiological principle that metabolic rate is primarily determined by the amount of metabolically active tissue.
Maintenance Calorie Estimates:
Four standard activity multipliers are applied to the BMR:
Worked Example
Consider a 70 kg male at 170 cm tall, using the estimation mode to calculate LBM via the Boer formula:
Male Boer formula: LBM = (0.407 × 70) + (0.267 × 170) – 19.2
Step by step: 28.49 + 45.39 – 19.2 = 54.68 kg LBM.
Katch-McArdle BMR: 370 + (21.6 × 54.68) = 370 + 1,181.09 = 1,551.09, rounded to 1,551 kcal/day.
Equation display: “BMR = 370 + (21.6 × 54.7) = 1,551 kcal/day”
Maintenance calories: sedentary = 1,861 kcal, light = 2,133 kcal, moderate = 2,404 kcal, very active = 2,676 kcal.
Now consider the same individual but with a known body fat percentage of 20%:
LBM = 70 × (1 – 0.20) = 56.0 kg.
BMR = 370 + (21.6 × 56.0) = 370 + 1,209.6 = 1,579.6, rounded to 1,580 kcal/day.
The small difference between the Boer estimate (54.68 kg LBM) and the body fat method (56.0 kg LBM) produces a BMR difference of about 29 calories—well within the typical margin of error for predictive equations.
This example demonstrates how the Katch-McArdle equation’s simplicity—one constant plus one coefficient times LBM—makes it transparent and easy to understand, while its focus on lean mass makes it more individualized than weight-only formulas.
Benefits of Using This Katch-McArdle Calculator
Accounts for body composition differences that weight-only equations miss.
Offers three flexible input modes for LBM determination.
Displays the exact equation with substituted values for educational clarity.
Provides maintenance calorie estimates at four activity levels.
Free and private, with all calculations running in your browser.
Supports both metric and imperial units.
FAQs
How accurate is the Katch-McArdle equation?
When accurate LBM measurements are used, Katch-McArdle is among the most accurate BMR equations, especially for athletic or muscular individuals. With estimated LBM, accuracy depends on the estimation method.
What is the Boer formula and how reliable is it?
The Boer formula estimates LBM from weight, height, and sex. It provides a reasonable population-level estimate but may be off by several kilograms for individuals with unusually high or low muscle mass.
Do I need a DEXA scan to use this calculator?
No. You can estimate LBM using the Boer formula mode or calculate it from your body fat percentage. Direct measurement improves accuracy but is not required.
Why doesn’t the Katch-McArdle equation use age?
The equation assumes that age-related metabolic changes are captured by changes in lean body mass. A person who maintains their LBM as they age would have the same predicted BMR.
Can I use this calculator if I am overweight?
Yes. Weight-based equations tend to overestimate BMR for individuals with higher body fat percentages. Katch-McArdle, using LBM, may provide a more accurate estimate in these cases.
How do I find my body fat percentage?
Body fat can be estimated using bioelectrical impedance scales, skinfold calipers, DEXA scans, or hydrostatic weighing. Consumer smart scales provide reasonable estimates for tracking changes over time.
Does this calculator store my personal data?
No. All calculations run entirely in your browser. No personal health or body composition data is saved or transmitted.
Can I share my Katch-McArdle results?
Yes. Use the Copy button to copy all results, or the Share button to send a summary that includes your LBM, BMR, and maintenance calories.
Is this calculator a substitute for professional nutrition advice?
No. This tool provides estimates for educational purposes. Consult a registered dietitian or healthcare professional for personalized nutrition guidance.
What is a typical lean body mass for men and women?
For men, LBM typically ranges from 55–75 kg depending on height and muscularity. For women, typical LBM ranges from 38–55 kg. Individual values vary widely based on genetics, training, and body size.
