Lean Body Mass Calculator

About this tool

Boer + Hume + James formulas

Estimate lean body mass (LBM) using Boer + Hume + James formulas. Outputs fat-free mass, fat mass, body fat % + category. Standard formulas used in clinical nutrition.

RT-HLT-018 · Health & Fitness

Gender

Weight (kg)

Height (cm)

Lean Body Mass (avg of 3 formulas)

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Estimated fat mass

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Estimated body fat %

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Boer

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Hume

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James

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Enter weight, height, and gender to compute lean body mass

How to use the Lean Body Mass Calculator

Enter weight, height, and gender

Weight in kg, height in cm, biological gender (male/female — formulas use gender-specific constants). For best accuracy, weigh first thing in the morning + measure height barefoot against a wall.

Read estimated lean body mass

Headline = average of Boer + Hume + James formulas. This is your estimated fat-free mass: muscle, bone, organs, water. Total weight − LBM = estimated fat mass.

Use LBM for nutrition + training calculations

LBM is the better baseline for: (1) BMR + TDEE (Katch-McArdle formula uses LBM); (2) protein intake (target 1.6-2.2g per kg LBM); (3) tracking body composition changes during cutting/bulking.

For precision, get a DEXA or BodPod scan

Formulas estimate within ±5-10%. DEXA scans (gold standard) are accurate to ±2%, cost $150-300 in most major ASEAN cities. BodPod and hydrostatic weighing are similarly accurate. For routine tracking, formula estimates are fine; for serious body-composition work (bodybuilding contests, sports science), get a real scan.

Lean body mass — the better baseline for nutrition + training

Lean body mass (LBM) — also called fat-free mass — is your body weight minus fat: muscle, bone, water, and organs. It\'s the metric clinical nutritionists and sports scientists use for accurate energy expenditure + protein intake calculations. Two people with the same total weight can have vastly different LBM: a 75kg muscular athlete might have 65kg LBM (10kg fat), while a 75kg sedentary office worker might have 55kg LBM (20kg fat). Their TDEE, protein needs, and body composition goals look completely different — but BMI treats them identically. LBM gives you the real picture.

The three formulas + when to use them

Boer formula (1984): most widely-used in clinical settings; accurate across normal-BMI adults. Hume formula (1966): older, slightly more conservative; preferred for elderly + chronically ill populations. James formula (1976): uses a quadratic relationship between weight and height; better at extremes (very tall, very short, very muscular). This tool averages all three for a balanced estimate. Individual formula divergence is usually within 2-3kg; large divergence (5kg+) suggests your inputs are at the edge of formula accuracy — get a DEXA scan if precision matters.

Most accurate calorie + protein math uses LBM, not total weight. Two people at 75kg can have 10kg different LBM — completely different nutritional needs.

How LBM drives nutrition + training

(1) Calorie targeting: the Katch-McArdle BMR formula (BMR = 370 + 21.6 × LBM kg) is generally more accurate than Mifflin-St Jeor (which uses total weight) for trained athletes + lean populations. For example, two 80kg lifters with different LBM (70kg vs 60kg) need different daily calories. (2) Protein needs: protein recommendations scale with LBM, not total weight. Target 1.6-2.2 g/kg LBM for strength + hypertrophy training (Phillips, Helms, Aragon meta-analyses). For 70kg LBM, that\'s 112-154g protein/day. (3) Body composition tracking: scale weight alone misleads — could be water, muscle, or fat changes. LBM change = muscle change; total weight change minus LBM change = fat change. Monthly LBM tracking shows whether your nutrition + training are actually producing the desired body composition shifts. (4) Performance prediction: in many sports, performance correlates more strongly with LBM than total weight (running, cycling, jumping).

The ASEAN body composition reality

Asian populations show higher body fat percentages at lower BMI than Western populations (the TOFI phenomenon — "thin outside, fat inside"). A 70kg Asian male with BMI 22 might have 22% body fat (55kg LBM); his Caucasian counterpart at the same BMI might have 17% body fat (58kg LBM). Same BMI, different LBM, different nutrition + health risk profiles. WHO Asian BMI thresholds are tighter (overweight 23+, obese 27.5+) partly because of this. For ASEAN adults: LBM tracking is especially useful — it bypasses BMI distortion and shows direct muscle changes. Lab body comp testing across ASEAN: DEXA at SingHealth + KKH + Mount Elizabeth (SG, ~$200-400); KPJ + Sunway Medical (MY); various sports clinics across Bangkok, Manila, Jakarta. Consumer alternatives: Omron + Tanita bioimpedance scales widely available ($100-300); Inbody analysers at most large gyms; skinfold calipers for self-measurement with technique training.

10 Things to Know About Lean Body Mass

LBM = body weight − fat. Includes muscle, bone, water, organs. Better baseline than total weight for nutrition + training.

Boer formula (1984) is the most widely-used clinical LBM estimation method.

Two people at same weight can have 10kg different LBM — completely different calorie + protein needs.

Katch-McArdle BMR uses LBM (not weight) — more accurate for trained athletes + lean populations.

Protein target: 1.6-2.2g per kg LBM for strength/hypertrophy. NOT per kg total weight (over-targets for higher body fat).

DEXA scan is gold standard (±2% accuracy). Formulas estimate within ±5-10%.

Asian populations show higher body fat at lower BMI (TOFI). LBM tracking bypasses BMI distortion.

LBM is muscle, not total mass. Bodybuilders + athletes maximise LBM; minimising fat is secondary.

LBM gains for trained lifters: ~250g/month optimal (Aragon + Schoenfeld 2013). Faster gains add fat, not muscle.

LBM declines ~3-5% per decade after 30 without training (sarcopenia). Strength training reverses this.

Frequently Asked Questions

Two people at the same weight can have vastly different body compositions. LBM gives you the metabolically active mass — what actually burns calories, needs protein, and drives strength + performance. Using total weight overestimates calorie + protein needs for high-body-fat people, and underestimates them for muscular people. LBM normalises across body compositions.
Boer for general adults; Hume for elderly; James for extreme heights. This tool averages all three for a balanced estimate. Divergence between formulas is usually 2-3kg max; if you see wider spread (5kg+), your body type is at the edge of formula accuracy — consider DEXA scan for precision. For routine tracking, the average is fine.
±5-10% of true LBM for most normal-BMI adults. Less accurate for: very muscular (underestimates LBM by 10-20%), obese (overestimates LBM by 10-20%), elderly with low LBM (variable). For body composition precision (competition prep, sports science research), use DEXA scan ($150-300, ±2% accuracy) or BodPod (~±3%). For routine self-tracking, formula estimates are sufficient — track the TREND, not absolute precision.
1.6-2.2g per kg LBM (not per kg total weight). Meta-analyses (Phillips, Helms, Morton) consistently support this range for strength + hypertrophy. Lower end (1.6g): maintenance + recreational training. Mid (1.8-2.0g): active cutting (calorie deficit) — preserves muscle. Higher end (2.0-2.2g): contest prep, very aggressive cuts. Going above 2.2g shows no additional benefit. For 70kg LBM: 112-154g protein/day across 3-5 meals.
Realistic LBM gain rates (Aragon + Schoenfeld 2013, Helms meta-analyses): Year 1 (novice): 7-10kg LBM possible with consistent training + nutrition; ~250-300g/week peak. Year 2-3 (intermediate): 3-5kg LBM/year; ~50-100g/week. Year 3+ (advanced): 1-3kg LBM/year; very slow. Past genetic ceiling: maintenance becomes the goal. Faster claimed gains usually = water + glycogen + measurement error. Real lean muscle gain is slow and grinding.
Depends on current body fat %. If body fat under 15% (M) / 25% (W): lean bulk first to build muscle base, then cut. If 15-20% (M) / 25-30% (W): either works — pick the one you\'re more motivated to do well. If above 20% (M) / 30% (W): cut first to improve hormonal environment + visual feedback motivation, then lean bulk. Body recomposition (simultaneous muscle gain + fat loss) is possible for true novices + post-layoff returners; impossible for trained intermediates without exogenous interventions.
Sarcopenia = age-related muscle loss. ~3-5% LBM loss per decade after age 30 without training; accelerates to 5-10%/decade past 65. By 80, untrained adults often have lost 30-50% of peak muscle mass. Prevention: resistance training (2-3 sessions/week) + adequate protein (1.2-1.6g/kg LBM for older adults). Studies (Phillips, Wolfe) show even adults starting strength training in their 60s + 70s reverse sarcopenia + gain LBM. Strength training is the closest thing to a longevity drug.
Ranked by accuracy: (1) DEXA scan: ±2% — gold standard, $150-300, in major hospital + sports clinics. (2) Hydrostatic weighing: ±2-3% — accurate but rare these days. (3) BodPod (air displacement): ±3%, $100-200. (4) Skinfold calipers: ±3-5% in trained hands; ±10%+ in untrained hands. (5) Bioimpedance scales (Omron, Tanita, Withings): ±5-8% — convenient but hydration-sensitive. (6) InBody devices (mid-tier bioimpedance at most large gyms): ±5-7%. For monthly tracking, bioimpedance is convenient; for serious body composition assessment, DEXA every 3-6 months.
No. All calculations run in your browser via JavaScript. Open DevTools → Network and confirm zero outbound requests. Weight, height, gender stay on your device. Safe for personal health tracking.
Pair with: BMI Calculator (RT-HLT-001) for cross-reference; Body Fat Calculator (RT-HLT-004) for additional body fat estimates; Waist-to-Height Ratio (RT-HLT-017) for cardiovascular risk; TDEE Calculator (RT-HLT-002) for caloric needs using LBM-based Katch-McArdle. External: DEXA scan booking via local hospitals; bioimpedance scales (Withings Body+, Omron HBF-516B, Tanita BC-587); InBody at major gym chains; skinfold caliper training resources (NASM, ACSM).

Lean Body Mass Calculator