Estimate how much of your weight is lean tissue. This free lean body mass calculator uses the Boer and James formulas to show your lean mass, fat mass and approximate body fat percentage.
An estimate from height, weight and sex – formulas can’t see your actual body composition. For precise measurement, methods like DEXA and professional guidance are best.
How Lean Body Mass Calculator Works
This tool estimates how much of your body weight is lean tissue (muscle, bone, organs, and water) versus fat, using your height, weight, and sex. It’s a formula-based estimate for general awareness, not a body composition scan.
Formula (Boer, displayed as the main result): Male LBM (kg) = 0.407 × Weight (kg) + 0.267 × Height (cm) − 19.2. Female LBM (kg) = 0.252 × Weight (kg) + 0.473 × Height (cm) − 48.3. Fat mass (kg) = Weight (kg) − LBM (kg), with a minimum of 0. Body fat % = (Fat mass ÷ Weight) × 100. The calculator also shows a second estimate using the James formula for comparison.
- Sex — male or female, since each formula uses different constants
- Units — metric (cm and kg) or imperial (ft/in and lb)
- Height — your height, entered in cm or ft/in
- Weight — your body weight, entered in kg or lb
Example Scenarios
| Sex | Height | Weight | Lean body mass (Boer) |
|---|---|---|---|
| Male | 178 cm | 75 kg | 58.9 kg |
| Female | 165 cm | 60 kg | 44.9 kg |
| Male | 183 cm | 90 kg | 66.3 kg |
| Female | 170 cm | 65 kg | 48.5 kg |
| Male | 170 cm | 68 kg | 53.9 kg |
Lean Body Mass Calculator FAQ
What’s the difference between the Boer and James formulas?
Both estimate lean body mass from height, weight, and sex, but use different constants derived from different research populations. The calculator displays the Boer formula as the main result and shows the James formula alongside it, since the two can differ by a kilogram or more for the same inputs.Why does lean body mass differ from muscle mass?
Lean body mass includes everything that isn’t fat — muscle, but also bone, organs, and body water. Muscle mass is only one part of that total, so your lean body mass number will always be higher than your muscle mass alone.How is body fat percentage estimated from lean body mass?
The calculator subtracts lean body mass from your total weight to get an estimated fat mass, then divides that by your total weight and multiplies by 100. It’s a derived estimate, not a direct measurement of fat.Can this calculator diagnose obesity or a body composition disorder?
No. It only applies a mathematical formula to height, weight, and sex, and cannot assess your actual body composition or health status. Any concerns about weight or body composition are best discussed with a healthcare professional.How accurate is a formula-based lean body mass estimate?
These formulas are population averages and don’t account for individual differences in bone density, muscularity, or fat distribution. For a precise measurement, methods like DEXA scans or other clinical body composition tools are more reliable than any formula.Does the calculator work with imperial units like pounds and feet/inches?
Yes. You can switch to imperial units and enter height in feet and inches and weight in pounds; the calculator converts these to centimeters and kilograms internally before applying the Boer and James formulas.Related Calculators
For a fuller picture of body composition, try the body fat calculator for another way to estimate fat percentage, the muscle mass calculator to focus specifically on muscle, or the BMI calculator to see how your height and weight compare on that separate scale.