Lean Body Mass Calculator
Calculate your lean body mass — everything in your body except fat tissue.
About Lean Body Mass
Lean Body Mass (LBM) = total weight minus fat mass. Calculated with the Boer formula — the most accurate for most adults. LBM includes muscle, bone, organs, skin, and water. Tracking LBM helps you assess muscle gain/loss independent of fat changes.
Accuracy The Boer formula estimates LBM within ±2–4 kg for most average-build adults. It may underestimate LBM in athletes with high muscle mass and overestimate in very sedentary individuals. For precise measurement, DEXA (dual-energy X-ray absorptiometry) scanning or hydrostatic weighing are the gold standards.
Boer Formula
| Sex | Formula |
|---|---|
| Male | 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 |
| Female | 0.252 × weight(kg) + 0.473 × height(cm) − 48.3 |
What to do with your result
- Use your LBM to set a protein target — multiply your LBM in kg by 1.6–2.2 g to get the ideal daily protein range for muscle preservation or growth.
- Track LBM monthly rather than total body weight — this reveals whether you are gaining muscle or losing fat even if the scale barely moves.
- Add progressive resistance training 3–4 days/week to increase LBM over time; aim for compound lifts (squats, deadlifts, presses, rows).
- Avoid aggressive calorie deficits below 500 kcal/day to protect LBM during weight loss — large deficits cause muscle breakdown alongside fat loss.
Frequently Asked Questions
What is lean body mass and what does it include?
Lean body mass (LBM) is everything in your body except fat — it includes skeletal muscle, bones, organs, skin, blood, and water. For a 70 kg person with 20% body fat, LBM would be 56 kg. LBM is important for understanding body composition because two people can weigh the same but have very different health profiles depending on their muscle-to-fat ratio.
What is the Boer formula and how accurate is it?
The Boer formula estimates LBM from height and weight: for males, LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2; for females, LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. It is considered more accurate than older formulas (James, Hume) for most adults, with typical error of ±2–4 kg. It does not account for individual muscle mass variation, so athletes or very sedentary individuals may see larger errors.
Why is lean body mass important for fitness and health?
LBM is directly linked to metabolism — muscle tissue burns more calories at rest than fat tissue. Higher LBM means higher BMR, making weight management easier. LBM also predicts strength, physical function, and independence in older age. Preserving LBM during weight loss (through sufficient protein and resistance training) is key to maintaining a healthy metabolic rate.
How can I increase my lean body mass?
The most effective strategy to increase LBM is progressive resistance training (strength training) 3–4 times per week combined with adequate protein intake (1.6–2.2 g/kg body weight). A modest calorie surplus of 200–300 kcal above TDEE supports muscle growth. Compound movements (squats, deadlifts, bench press, rows) maximize muscle stimulus. Allow 48 hours rest for each muscle group between sessions.
What is the difference between lean body mass and muscle mass?
Lean body mass includes all non-fat tissue: muscle, bones, organs, skin, and fluids. Muscle mass is just the skeletal muscle component — typically 40–50% of LBM in healthy adults. So a person with 60 kg LBM might have 25–30 kg of actual muscle mass. Body composition scans like DEXA can separate these components, while formulas like Boer only estimate total LBM.
This calculator is for educational purposes only. Consult a qualified healthcare professional for medical advice.