Lean Body Mass Calculator — LBM & Fat Mass

Lean body mass (LBM) is the weight of everything in your body except fat — muscles, bones, organs, water, and connective tissue. LBM = Total Weight × (1 − Body Fat Fraction). For example, a 75 kg person with 20% body fat has LBM = 75 × 0.80 = 60 kg.

For men: 6–13% (athletic), 14–17% (fit), 18–24% (average), 25%+ (obese). For women: 14–20% (athletic), 21–24% (fit), 25–31% (average), 32%+ (obese). Women naturally carry more essential fat than men due to hormonal and reproductive physiology.

Common methods: DEXA scan (most accurate), hydrostatic weighing, skin fold calipers (trained practitioner), bioelectrical impedance (home scales — moderate accuracy). For a rough estimate, use the US Navy tape measure method based on waist, neck, and hip circumference.

LBM determines your basal metabolic rate (BMR) — more muscle means higher calorie burn at rest. Athletes focus on maintaining or increasing LBM while reducing fat mass. LBM is also important for medication dosing and assessing athletic performance.

Yes, but it requires a modest calorie deficit (not more than 500 calories/day), adequate protein intake (1.6–2.2g per kg of body weight), and resistance training. A steep calorie deficit causes muscle loss alongside fat loss, reducing your LBM and lowering metabolism.