By Zencalcy Editorial TeamLast reviewed About us
The Katch-McArdle equation estimates basal metabolic rate from lean body mass rather than total body weight. Because lean tissue drives most resting energy use, this approach can be more informative for people whose body composition differs strongly from average, such as athletes or people with a high body-fat percentage. This calculator reports lean body mass, BMR and a BMI reference.
Estimate BMR from lean body mass instead of total weight.
| Use a repeatable measurement method. |
LBM = weight x (1 - body fat / 100) BMR = 370 + 21.6 x LBM
LBM is lean body mass in kilograms and body fat is a percentage. The equation assumes that lean tissue has a predictable energy cost at rest. An inaccurate body-fat estimate will shift the result directly, so use the same measurement method when tracking changes.
| Symbol | Meaning |
|---|---|
| LBM | Lean body mass in kilograms, excluding fat mass. |
| body fat | Body-fat percentage of total weight. |
| BMR | Basal metabolic rate in kilocalories per day. |
LBM = 80 x (1 - 0.20) = 64 kg. BMR = 370 + 21.6 x 64 = 370 + 1382.4 = 1752.4 kcal per day. At 180 cm the same person has a BMI of 24.7, which is useful context but does not change the lean-mass calculation.
At rest, the body's energy use is dominated by organs and lean tissue rather than stored fat. That is the logic behind the Katch-McArdle equation: estimate the metabolically active mass, then apply an energy cost per kilogram. The approach is elegant, but its weak point is the body-fat input. Skinfold equations, consumer impedance scales and DEXA scans can disagree by several percentage points, and hydration, food and exercise can shift impedance readings within a day. If you use this calculator, choose one measurement method and repeat it under the same conditions. Track the trend in lean mass alongside strength and waist measurements. A falling BMR with stable weight may mean lean mass is being lost, which is worth addressing before cutting calories further.
Continue with the BMR Calculator (Mifflin-St Jeor), Harris-Benedict Calculator, or the RMR Calculator (Resting Metabolic Rate) — or browse more dietary tools and all health calculators.
Also see the Calorie Calculator, TDEE Calculator and the Macro Calculator.
Fat mass is metabolically quieter than lean tissue. Using total weight can overestimate BMR for people with high body fat and underestimate it for very muscular people. Lean mass gets closer to the tissue that actually consumes most resting energy.
Energy and nutrient estimates are population guidance, not personal prescriptions. Actual needs vary with body composition, medical conditions, medication, pregnancy and activity. Values are rounded and should be discussed with a registered dietitian or clinician when used to plan treatment.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026