CalcBMR Calculator (Katch-McArdle)
BMR Calculator (Katch-McArdle). Free online calculator with formula, examples and step-by-step guide.
Katch-McArdle BMR Calculator: metabolism from lean body mass
The Katch-McArdle formula estimates basal metabolic rate using lean body mass only, making it especially useful for people with very high or very low body fat percentages. This calculator takes your lean body mass in kilograms and returns an estimate of daily resting calories.
Katch-McArdle formula
The equation is the same for men and women as long as you use lean body mass (LBM), not total weight:
BMR = 370 + 21.6 · LBM
LBM is expressed in kilograms and represents your body weight minus fat mass. You can derive it from estimated body fat: LBM = total weight · (1 − body fat fraction).
Example 1: muscular individual
Problem: Total weight 80 kg, body fat 15 %.
- Lean body mass:
- LBM = 80 · (1 − 0.15) = 80 · 0.85 = 68 kg.
- BMR:
- BMR = 370 + 21.6 · 68 ≈ 370 + 1,468.8 ≈ 1,838.8 kcal/day.
Answer: BMR ≈ 1,839 kcal/day.
Example 2: higher body fat
Problem: Total weight 90 kg, body fat 30 %.
- Lean body mass:
- LBM = 90 · (1 − 0.30) = 90 · 0.70 = 63 kg.
- BMR:
- BMR = 370 + 21.6 · 63 ≈ 370 + 1,360.8 ≈ 1,730.8 kcal/day.
Answer: BMR ≈ 1,731 kcal/day.
Common uses of Katch-McArdle
- Designing diets for athletes with significant muscle mass.
- Planning fat‑loss programs that prioritize muscle preservation.
- Tuning calorie targets for bodybuilding, powerlifting or physique sports.
- Assessing how changes in body composition affect metabolism.
- Estimating TDEE starting from a BMR tightly linked to active tissue.
- Evaluating progress after major weight or body‑composition changes.
Common mistakes when using Katch-McArdle
- Using total body weight instead of lean body mass in the formula.
- Grossly over‑ or under‑estimating body fat percentage, which distorts LBM.
- Forgetting that the formula outputs BMR, not full daily calorie needs.
- Rounding body fat estimates unrealistically just to get "nice" numbers.
Pro tip
If you do not have precise body fat measurements (DXA, calipers, high‑quality BIA), combine several visual and measurement‑based estimates and update them every few weeks. Small errors in body fat do not ruin the calculation, but large misestimates can meaningfully affect your calorie planning.
It tends to be more accurate for people whose body composition differs strongly from average, because it focuses on lean mass, which drives most resting energy expenditure. Accuracy still depends on how well you estimate body fat.
You need your total body weight and an estimate of your body fat percentage. Then compute LBM = weight · (1 − body fat fraction). Many scales and anthropometric assessments provide an approximate body fat value.
No, the equation is identical. Sex differences are reflected in typical lean mass levels, not in different coefficients in the formula itself.
Yes, but first convert BMR to TDEE with an activity factor. Once you know your TDEE, add or subtract calories (for example ±10–20 %) depending on whether you want to gain or lose weight.