Lean Body Mass Calculator
Calculate lean mass and fat mass by method of your choice.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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This calculator offers two methods for estimating lean body mass (LBM), which is everything in your body except stored fat.
- Body fat percentage method. If you know your body fat percentage from a DEXA scan, skinfold calipers, or an impedance scale, enter your weight and body fat percentage. LBM = weight × (1 − body fat / 100). This is the most direct calculation.
- Boer formula. If you do not have a body fat measurement, the Boer formula estimates LBM from weight and height alone. For males: 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. For females: 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. Enter your weight and height in the appropriate unit.
About Lean Body Mass
Lean body mass includes muscle, bone, organs, skin, water, and all other fat-free tissues. It is distinct from fat-free mass (FFM) in that LBM includes a small amount of essential fat (roughly 2 to 5 percent in men and 10 to 13 percent in women) that is required for basic physiological function.
LBM is the primary driver of resting metabolic rate (RMR). Higher LBM means more calories burned at rest. It is used in calculating TDEE, drug dosing, nutrition planning, and FFMI. During weight loss, preserving LBM through resistance training and adequate protein intake is the primary goal, since fat mass is the target for reduction.
Frequently Asked Questions
What is a good lean body mass percentage?
Lean mass percentage is simply 100 minus body fat percentage. For males, lean mass percentages of 82 to 90 percent (body fat 10 to 18 percent) are in the fitness to athletic range. For females, 75 to 86 percent lean (14 to 25 percent body fat) covers fit to athletic. Elite bodybuilders in competition condition may reach 94 to 97 percent lean, but these levels are not sustainable long-term. Essential body fat alone accounts for 2 to 5 percent in men and 10 to 13 percent in women.
What is the Boer formula and how accurate is it?
The Boer formula was derived by Boer (1984) using regression analysis of measured lean body mass in a clinical population. It uses weight and height as predictors since these correlate with bone and muscle mass. Accuracy is moderate but can be off by 3 to 5 kg for individuals with unusual body compositions (very obese, very lean, or heavily muscled). For most people of average build it provides a reasonable estimate without requiring any body fat measurement equipment.
How does lean body mass affect metabolism?
Skeletal muscle burns approximately 6 calories per pound per day at rest, compared to roughly 2 calories per pound for fat tissue. Organs are metabolically even more active. This means that two people of the same total weight but different body compositions can have resting metabolic rates that differ by 200 to 400 calories per day. Building and maintaining lean mass through strength training is one of the most effective long-term strategies for metabolic health.
How is lean body mass used in medication dosing?
Many medications are dosed based on lean body mass rather than total body weight to avoid over-dosing in patients with high body fat, since fat tissue does not absorb water-soluble drugs as efficiently as lean tissue. This is particularly relevant for antibiotics, anesthetics, and chemotherapy agents. The Devine and Boer formulas were originally developed precisely for this clinical purpose. When a pharmacist or physician specifies dosing based on "ideal weight" or "adjusted weight," they are using a variation of LBM estimation.