Boer · James · Hume Formulas · 2026

Lean Body Mass Calculator

Calculate your Lean Body Mass (LBM) using three validated medical formulas: Boer, James, and Hume. See fat mass, body composition bar, and protein needs based on your lean mass.

Last updated

3 Formula Comparison
Body Composition Bar
Protein Needs by LBM
Metric & Imperial
Our networkfavorit5The 5 worth buying.Top fives, comparisons and what reviewers say.See the top 5s
Lean Body Mass Calculator
Boer · James · Hume Formulas
ft
in
lbs
%
If known, overrides formula estimates. Use body fat calculator to find yours.
💪

Enter your height and weight to calculate lean body mass.

Our networkLegalCost.usLegal costs, calculated for your stateChild support, alimony, DUI fines and injury settlements. Free and instant.Open LegalCost.us
Our networkdiscount5Fresh deals. Five at a time.Only the offers worth a click, with the ones ending soonest on top.Price dropsCoupon codesClearance and flash salesFree shipping offersSee today’s dealsEnding soonest first.

What Is Lean Body Mass?

By the Boer formula, a 5'10" man who weighs 180 lb has about 136 lb (61.5 kg) of lean body mass, or 75% of his weight. Lean mass is everything that is not fat: muscle, bone, organs and water. Enter your height, weight and sex above to compare the Boer, James and Hume estimates, or add a known body fat percentage for a direct result.

Lean Body Mass (LBM) is everything in your body that is not fat: muscles, bones, organs, water, connective tissue, and skin. It is sometimes called Fat-Free Mass (FFM), though strictly speaking LBM may include a small amount of essential fat in bone marrow and organs (approximately 3% in men, 12% in women), while FFM includes none.

LBM matters more than total body weight for most health and performance metrics. Drug dosing, protein targets, BMR calculations using the Katch-McArdle formula, and athletic performance planning all use LBM rather than total weight. Knowing your lean mass helps you set evidence-based protein targets and track the quality of your body composition changes over time.

FormulaYearMen (kg)Women (kg)Notes
Boer19840.407W + 0.267H − 19.20.252W + 0.473H − 48.3Most widely used clinically
James19761.1W − 128(W/H)²1.07W − 148(W/H)²Based on TBW measurements
Hume19660.32810W + 0.33929H − 29.53360.29569W + 0.41813H − 43.2933Oldest, slightly lower estimates

W = weight (kg), H = height (cm). If you know your body fat %, LBM = Total Weight × (1 − BF%).

LBM vs Fat-Free Mass

LBM and FFM are often used interchangeably but differ slightly. FFM is truly all non-fat tissue. LBM includes a small amount of essential body fat located in bone marrow, cell membranes, and organs (about 3% in men, 10-12% in women). In practice, most clinical formulas calculate LBM, and the distinction rarely matters for fitness or nutrition purposes.

Why LBM Matters for Protein

Some coaches and dietitians set protein per kg of lean body mass rather than total body weight. A 200 lb man with 30% body fat has ~140 lbs of LBM and needs protein based on that. Setting protein targets based on total weight overestimates needs for heavier people with high body fat. Most studies behind the 1.6 to 2.2 g/kg range for muscle gain used total body weight, so an LBM-based target is the conservative end.

Tracking LBM Over Time

Scale weight alone is a poor indicator of progress. During a fat loss phase, tracking LBM allows you to verify you are losing fat rather than muscle. During a muscle-building phase, LBM gain confirms hypertrophy. DEXA scans every 3-6 months provide the most accurate tracking. Navy method body fat calculations provide a practical free alternative for estimating LBM trends over time.

LBM and Drug Dosing

Many medications are dosed based on LBM or ideal body weight rather than total body weight to avoid toxicity in obese patients. This is especially important for renally-cleared drugs, chemotherapy agents, anesthetic agents, and aminoglycoside antibiotics. The Devine formula for ideal body weight and Boer formula for LBM are the most commonly used in clinical pharmacology and pharmacy practice.

Worked Example: All Three Formulas

W is weight in kg and H is height in cm. For a man who is 5'10" (177.8 cm) and 180 lb (81.65 kg):

  • Boer: 0.407 × 81.65 + 0.267 × 177.8 − 19.2 = 61.5 kg (136 lb)
  • James: 1.1 × 81.65 − 128 × (81.65 ÷ 177.8)2 = 62.8 kg (138.5 lb)
  • Hume: 0.32810 × 81.65 + 0.33929 × 177.8 − 29.5336 = 57.6 kg (127 lb)

For a woman who is 5'5" (165.1 cm) and 140 lb (63.5 kg), the women's equations give 45.8 kg (101 lb) with Boer, 46.1 kg (101.5 lb) with James and 44.5 kg (98 lb) with Hume, whose women's formula is 0.29569W + 0.41813H − 43.2933.

If you know your body fat, skip the formulas: LBM = weight × (1 − body fat %). At 180 lb and 20% body fat that is 144 lb.

Lean Body Mass Chart (Boer Formula)

Estimated lean body mass by height and weight, computed with the same Boer formula the calculator uses, rounded to the nearest pound.

Men

Height150 lb180 lb210 lb240 lb
5'6"117 lb130 lb142 lb154 lb
5'10"123 lb136 lb148 lb160 lb
6'2"129 lb142 lb154 lb166 lb

Women

Height120 lb140 lb160 lb180 lb
5'2"88 lb93 lb98 lb103 lb
5'5"96 lb101 lb106 lb111 lb
5'8"104 lb109 lb114 lb119 lb

The formulas assume an average build. Someone who lifts weights will usually have more lean mass than the chart shows, and someone who is inactive may have less.

Where the Formulas Break Down

The James formula at high body weight

Because James subtracts a squared term, its estimate stops rising and then falls as weight goes up. For a 5'5" woman it peaks at about 217 lb and drops after that: at 300 lb it gives only 99 lb of lean mass, while Boer gives 141 lb. For a 5'10" man the peak comes at about 299 lb. Above those weights, ignore the James result.

Protein targets

The RDA of 0.8 g of protein per kg is set on total body weight. The 1.6 to 2.2 g/kg range often quoted for strength training also comes from studies per kg of body weight. Working from lean mass gives lower, more conservative numbers, which some dietitians prefer for people with a lot of body fat. A registered dietitian can tell you which basis suits you.

These are estimates, not a diagnosis. For drug dosing or medical decisions, your care team will use its own methods. To estimate the body fat percentage you can enter above, try the body fat calculator.

Method and sources. Boer P (1984), James WPT (1976) and Hume R (1966, J Clin Pathol) lean body mass equations, with W in kg and H in cm; 1 kg = 2.20462 lb. Every example and table value was computed with the same equations the calculator uses. Protein RDA: National Academies Dietary Reference Intakes. Muscle energy use of about 13 kcal/kg a day: Elia (1992) organ and tissue metabolic rates. Estimates only, not medical advice.
LBM estimates from height/weight formulas carry an error margin of approximately 3-5 kg. Body fat percentage-based calculation (if known) is significantly more accurate. This is not medical advice. Consult a healthcare professional for clinical applications.
Our networkLegalCost.usWhat will your legal case cost?Official formulas for all 50 states. Free, no signup.Check your state

Lean Body Mass Questions

Lean body mass (LBM) is your total body weight minus fat mass. It includes all muscle, bone, organs, connective tissue, skin, and body water. LBM matters because it is the metabolically active component of your body that drives your basal metabolic rate, determines your strength and functional capacity, and sets your protein requirements. People with higher LBM have higher BMR, burn more calories at rest, and tend to have better metabolic health markers. Tracking LBM is more meaningful than tracking total weight because it separates the beneficial mass (muscle, bone) from the metabolically problematic mass (excess fat).

Several validated formulas estimate LBM from height and weight alone. The three most common are: Boer (1984), which is the most widely used clinically; James (1976), based on total body water measurements; and Hume (1966), the oldest formula. All three use height (cm) and weight (kg) with different constants for men and women. The formulas typically agree within 2-4 kg of each other. If you know your body fat percentage (from a DEXA scan, Navy method, or calipers), a more accurate method is: LBM = Total Weight × (1 − Body Fat %).

There is no single "healthy LBM" number: it depends on height, sex, and age. Instead, a useful approach is to target a body fat percentage that reflects your goals, then calculate the resulting LBM. For men: athletic/fitness level LBM corresponds to 83-93% of total body weight (body fat 7-17%). For women: fitness level LBM corresponds to 76-86% of total body weight (body fat 14-24%). More practically: aim to maximize LBM through progressive resistance training and adequate protein while keeping body fat in a healthy range. LBM naturally declines with age (sarcopenia), so maintaining lean mass becomes increasingly important after age 40.

Lean body mass is a broader category that includes everything that is not fat: muscle, bone, organs, blood, skin, and connective tissue. Muscle mass is just the skeletal muscle component of LBM. Skeletal muscle typically accounts for 35-45% of total body weight in healthy adults and 55-65% of LBM. Other components of LBM include bone mineral (about 15% of LBM), organs and viscera (about 15%), blood and extracellular fluid (about 10-15%), and skin and connective tissue (about 5-10%). When people talk about "gaining muscle," they mean increasing skeletal muscle within LBM, not LBM as a whole.

Research supports the following protein targets based on LBM: Minimum for muscle preservation during a calorie deficit: 1.6g per kg of LBM per day. Optimal for muscle building and performance: 1.6-2.2g per kg of LBM per day. Higher end for during aggressive calorie restriction or very high training volumes: up to 2.4-3.1g per kg of LBM. Example: a 90 kg man with 20% body fat has 72 kg of LBM. Optimal protein: 72 × 1.6 = 115g to 72 × 2.2 = 158g per day. Note: some researchers prefer using target body weight rather than current LBM for protein calculations in obese individuals, as LBM formulas become less accurate at very high body weight.

Yes. Skeletal muscle (the largest component of LBM) can be increased through progressive resistance training combined with adequate protein intake and a slight calorie surplus. Bone density (another LBM component) increases with weight-bearing exercise, particularly resistance training and impact sports. Organ mass is largely fixed and not meaningfully changeable. Practical approach for increasing LBM: progressive overload resistance training 3-5 days per week, protein intake of 1.6-2.2g per kg of LBM, a modest calorie surplus of 200-400 calories above TDEE, adequate sleep (growth hormone peaks during deep sleep), and patience, natural muscle building rates are 0.5-2 lbs per month for most people under optimal conditions.

LBM naturally declines with age through a process called sarcopenia (age-related muscle loss). After age 30, adults lose approximately 3-8% of muscle mass per decade, accelerating to 15% per decade after age 70 without intervention. Bone density also begins declining around age 30-35, particularly in women after menopause. This age-related LBM decline reduces BMR (making weight management harder), decreases functional strength and mobility, and increases fall/fracture risk. The most effective interventions: progressive resistance training (the most potent stimulus for maintaining muscle), adequate protein (at least 1.2-1.6g/kg total body weight in older adults), vitamin D and calcium for bone health, and avoiding prolonged sedentary periods.

Almost, but not exactly. Fat-free mass (FFM) refers to the total mass of the body excluding all fat tissue, including essential fat. Lean body mass (LBM) typically includes a small amount of essential fat stored in bone marrow, cell membranes, and organs (approximately 3% of LBM in men, 10-12% in women). This essential fat cannot be eliminated without compromising health. In practical use, the terms are often used interchangeably in fitness, nutrition, and most clinical contexts. The distinction becomes relevant primarily in precise research settings using reference methods like DEXA or the four-compartment model.

LBM is the primary determinant of BMR. The Katch-McArdle formula, considered the most accurate BMR formula for lean individuals, calculates: BMR = 370 + (21.6 × LBM in kg). This formula reveals that each kilogram of lean mass contributes approximately 21.6 calories to daily BMR. By comparison, fat tissue contributes approximately 4-9 calories per kg. This means people with higher LBM have significantly higher BMR and can eat more calories without gaining fat. By the Katch-McArdle equation, 5 kg more lean mass adds about 108 calories a day, though measured skeletal muscle burns closer to 13 calories per kg a day, or about 65 calories for 5 kg. This is the metabolic argument for resistance training as a long-term weight management strategy.

Height/weight-based LBM formulas (Boer, James, Hume) have an error range of approximately 3-6 kg when compared to reference methods. They tend to overestimate LBM in obese individuals and underestimate in very lean/muscular individuals. More accurate methods in descending order of precision: DEXA (dual-energy X-ray absorptiometry, gold standard, error <1-2 kg), four-compartment model (most precise but expensive), hydrostatic weighing (~1-3% error), BodPod air displacement plethysmography (~1-3%), Navy circumference method (~3-4%), bioelectrical impedance (BIA, ~4-8% depending on hydration), and height/weight formulas (~5-10%). If you know your body fat percentage from any of these methods, calculating LBM as Total Weight × (1 − BF%) is always more accurate than using the anthropometric formulas in this calculator.

Boer is the usual default and is the one this calculator shows first. James gives similar results at normal weights but falls apart at high body weight (above about 217 lb for a 5'5" woman). Hume tends to come out a few pounds lower than both. If you know your body fat percentage from DEXA or a tape method, LBM = weight × (1 − body fat %) beats all three.

It depends on height. By the Boer formula a 180 lb man has about 130 lb of lean mass at 5'6", 136 lb at 5'10" and 142 lb at 6'2", which is 72% to 79% of his weight. A trained lifter at the same weight may have more; a man at 180 lb and 15% body fat has 153 lb of lean mass.
More Health Calculators
Body Fat Calculator
Health
BMI Calculator
Health
BMR Calculator
Health
Calorie Calculator
Health
Macro Calculator
Health
Ideal Weight
Health
Calorie Deficit
Health
Water Intake
Health
Running Pace
Health
Sleep Calculator
Health