Lean Body Mass Calculator
Find out how much of your weight is lean tissue — muscle, bone, and organs — versus fat. A smarter measure of body composition than the scale alone.
What is lean body mass?
Lean body mass (LBM) — also called fat-free mass — is the total weight of everything in your body except fat. This includes skeletal muscle, smooth muscle, bone, organs, blood, water, and connective tissue. It's a more informative health metric than total body weight because it reflects the tissues that drive your metabolism, produce strength, and support physical function.
Two people can have the same total weight and height but very different body compositions — one with high muscle mass and low body fat, the other the reverse. LBM reveals that difference where a simple scale reading cannot.
How lean body mass is calculated (Boer formula)
This calculator uses the Boer formula, which is widely regarded as the most accurate LBM estimation method available without body fat measurement equipment:
- Men: LBM = (0.407 × weight in kg) + (0.267 × height in cm) − 19.2
- Women: LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3
The Boer formula accounts for both weight and height, which improves accuracy over weight-only methods. Like all estimation formulas, it provides an approximation — the most accurate measurements come from DEXA scans or hydrostatic weighing, but these aren't accessible to most people.
Why lean body mass matters
It determines your metabolic rate
Lean tissue — particularly skeletal muscle — is metabolically active. The more LBM you carry, the more calories your body burns at rest. This is why two people of the same weight can have different caloric needs, and why building muscle is an effective long-term strategy for weight management.
It's a better fitness metric than weight
During body recomposition (losing fat while gaining or maintaining muscle), total body weight may barely change while body composition improves significantly. Tracking LBM alongside total weight gives a more complete picture of what's actually happening in your body.
It predicts physical function and longevity
Higher LBM — particularly muscle mass — is strongly associated with functional independence, fall prevention, and longevity, especially in adults over 50. Age-related muscle loss (sarcopenia) begins as early as the 30s and accelerates after 60; regular resistance training is the most evidence-backed strategy for maintaining LBM with age.
Average lean body mass by age and gender
| Age range | Avg LBM — Men | Avg LBM — Women |
|---|---|---|
| 20–29 | 61–68 kg (134–150 lb) | 42–48 kg (93–106 lb) |
| 30–39 | 62–70 kg (137–154 lb) | 43–49 kg (95–108 lb) |
| 40–49 | 61–69 kg (134–152 lb) | 42–48 kg (93–106 lb) |
| 50–59 | 59–67 kg (130–148 lb) | 41–47 kg (90–104 lb) |
| 60–69 | 57–65 kg (126–143 lb) | 40–46 kg (88–101 lb) |
These are estimates based on population averages. Athletic individuals will typically have higher LBM than the averages shown; sedentary individuals may be lower.
How to increase lean body mass
- Resistance training: Progressive overload through weight lifting, bodyweight exercise, or resistance bands is the primary stimulus for muscle growth. Aim for 2–4 sessions per week targeting all major muscle groups.
- Adequate protein intake: Muscle protein synthesis requires dietary protein. Research supports 1.6–2.2g per kg of bodyweight per day for muscle growth and preservation.
- Sufficient sleep: Growth hormone — which drives muscle repair and synthesis — is predominantly released during deep sleep. 7–9 hours per night optimises recovery.
- Consistency over time: Lean mass changes slowly. Expect months, not weeks, to see meaningful changes. Track LBM (not just weight) to see progress during body recomposition.