What is lean body weight (lean body mass)?

**Lean body weight (LBW)** or **lean body mass (LBM)** is total body weight minus fat mass. It includes **skeletal muscle**, **water**, **bone**, **organs**, connective tissue, and blood—everything that is not stored adipose tissue. It is **not** the same as **muscle mass alone** (muscle is roughly 40–50% of LBM in healthy adults). LBM is used in **body composition screening**, some **drug dosing** contexts (e.g. aminoglycosides historically), and **nutrition** planning when you want fat-free mass as a denominator.

How is lean body weight calculated without a DEXA scan?

This calculator uses **regression formulas** from **weight (kg)** and **height (cm)** and **sex**: **Boer (1984)** — most common default; **James (1976)** — weight-to-height ratio squared term; **Hume (1966)** — alternative coefficients. Example **Boer male**: LBM = 0.407×weight + 0.267×height − 19.2. **Implied body fat %** = (weight − LBM) ÷ weight × 100. These predict population averages—individual error vs **DEXA** is often **±3–5 percentage points** of body fat, wider in athletes and very lean or very high BMI individuals.

Which formula is best—Boer, James, or Hume?

No single formula wins for every body. **Boer** is widely cited in clinical teaching and usually the default here. **James** and **Hume** can differ by several kg LBM on the same person—see the **compare formulas** block in results. For important decisions (competition prep, clinical malnutrition), use **DEXA, BIA, BodPod, or repeated caliper** measures rather than picking whichever formula gives the lowest body fat. Consistency (same formula over time) matters more than one-off formula shopping.

What is a healthy lean body mass percentage?

Healthy **lean mass %** = 100 − body fat %. **ACE-style teaching ranges** (approximate): men **fitness** ~83–86% lean (14–17% fat), **athletic** ~87–94% lean (6–13% fat); women **fitness** ~76–79% lean (21–24% fat), **athletic** ~80–86% lean (14–20% fat). Essential fat floors exist (~3–5% men, ~8–12% women). **Older adults** often have lower LBM % even at “normal” BMI due to sarcopenia—age on this page adds context but does not change Boer/James/Hume math.

Lean body weight vs muscle mass—what is the difference?

**Muscle mass** refers mainly to **skeletal muscle** you can hypertrophy with resistance training. **LBM** is broader: it counts **bone mineral**, **viscera**, **plasma volume**, and **glycogen-bound water** that fluctuates day to day. Two people with identical LBM can differ in muscle size if one carries more organ mass or fluid. To emphasize **muscle** specifically, track **strength**, **limb circumference**, **ultrasound**, or **DEXA segmental lean**—not LBM formulas alone.

Is lean body weight better than BMI?

**BMI** (weight ÷ height²) ignores **fat vs muscle**. A muscular lifter can be **“overweight”** on BMI with healthy body fat; someone with **normal BMI** can carry high visceral fat (“normal weight obesity”). **LBM-derived body fat %** separates tissue types better than BMI alone but still **estimates** fat—it is not measured. Use **BMI** for population screening; use **LBM + waist** or **DEXA** when body composition drives your goal.

How do I increase lean body weight?

**Resistance training** 2–4×/week with progressive overload is the primary driver of muscle-containing LBM. **Protein** ~**1.6–2.2 g/kg/day** (clinician-adjusted if CKD) supports hypertrophy. A **small caloric surplus** (+200–300 kcal) helps gain; **recomposition** uses maintenance or slight deficit with high protein to lose fat while preserving LBM. **Sleep 7–9 h**, adequate **vitamin D**, and **creatine monohydrate** (3–5 g/day in many protocols) are common adjuncts. Rate of gain: often **0.25–0.5 kg** lean tissue per month in trained beginners—slower later.

Can I lose fat without losing lean body weight?

Yes—**body recomposition**. Strategies: **moderate deficit** (≈300–500 kcal/day), **high protein** (often ≥1.8 g/kg during cuts), **heavy lifting**, and **slow fat loss** (≈0.25–0.75% body weight per week). Rapid crash diets and excessive cardio without lifting increase **lean mass loss**. **Protein + resistance** preserves LBM in many trials; **elderly** and **low protein** groups lose more lean mass per kg fat lost.

What does “ideal lean body weight” mean on this calculator?

It is a **teaching estimate**: mid-range **healthy BMI** for your height → average “ideal” total weight, then subtracts an assumed **average body fat %** (~17.5% men, ~22.5% women) to get a **target LBM number**. It is **not** a medical prescription or maximum muscular potential. **FFMI** (fat-free mass index) and sport-specific goals differ. Use ideal LBW as a rough benchmark only.

Why do Boer, James, and Hume give different body fat percentages?

Each regression was fit on different **1970s–1980s cohorts** with different assumptions. **Hume** often reads **higher body fat %** than **Boer** on the same inputs (e.g. 70 kg, 175 cm male: Boer ~20% vs Hume ~25% in our compare table). None is “truth”—they are **approximations**. Pick one formula and track **trend** over months, or invest in **direct measurement** for absolute accuracy.

Does lean body weight include bone and water?

**Yes.** LBM includes **bone mineral**, **extracellular and intracellular water**, organs, and connective tissue. **Hydration** shifts daily LBM by kilograms without changing muscle protein. **Dehydration** after sauna or diuretics artificially lowers scale weight and can **distort** formula-implied body fat %. Weigh under **consistent conditions** (morning, post-bathroom) for tracking.

Is this lean body weight calculator medical advice?

**No.** Formula LBM is for **education and fitness planning**, not diagnosis of sarcopenia, cachexia, or eating disorders. **Children**, **pregnancy**, **amputation**, **edema**, and **hospitalized** patients need specialist assessment. Seek care for unintentional weight loss, weakness, or body composition concerns tied to illness.

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Body composition

Lean Body Weight Calculator

Estimate lean body weight (LBM) in kg with Boer, James, or Hume formulas, then see implied body fat %, BMI, and a three-formula comparison. Educational—DEXA or calipers measure fat more directly. More tools on our medical calculators hub.

Last updated: June 4, 2026

Boer, James & Hume with live comparison

Implied body fat % and ACE-style range context

Step-by-step formula display in results

Lean body weight calculator

Boer, James, or Hume LBM with implied body fat % — educational, not DEXA

Weight (kg)

Height (cm)

Sex (formula)

Age (years)

Formula

Results

Boer (1984) — common clinical estimate

Lean body weight

56.02 kg

Implied body fat

20%

(0.407×70) + (0.267×175) − 19.2 = 56.02 kg

Fat mass

13.99 kg

Lean %

80%

BMI

22.9 (Normal weight)

Ideal LBW (teaching)

56.85 kg

Compare formulas

Boer (1984) 56.02 kg · 20% BF

James (1976) 56.52 kg · 19.3% BF

Hume (1966) 52.81 kg · 24.6% BF

Solid fitness range—progressive overload 2–4×/week.

DEXA, BodPod, or calipers measure composition more directly—formulas are estimates.

Estimates only. Regression LBM is not DEXA. Athletes, pregnancy, edema, and clinical illness need professional body composition assessment—not formula body fat alone.

Example results (from calculator logic)

Male 70 kg · 175 cm · Boer

56.02 kg LBM

~20% implied fat · BMI 22.9

Female 65 kg · 165 cm

46.13 kg LBM

~29% implied fat

Male 75 kg · 175 cm

58.05 kg LBM

~22.6% implied fat

LBM formulas (equations)

Formula	Male	Female
Boer (1984)	LBM = 0.407×weight(kg) + 0.267×height(cm) − 19.2	LBM = 0.252×weight(kg) + 0.473×height(cm) − 48.3
James (1976)	LBM = 1.10×weight − 128×(weight/height)²	LBM = 1.07×weight − 148×(weight/height)²
Hume (1966)	LBM = 0.3281×weight + 0.33929×height − 29.5336	LBM = 0.29569×weight + 0.41813×height − 43.2933

Implied body fat % = (weight − LBM) ÷ weight × 100

ACE-style body fat & lean mass ranges (teaching)

Men

Athletic: 6–13% body fat · 87–94% lean mass
Fitness: 14–17% body fat · 83–86% lean mass
Average: 18–24% body fat · 76–82% lean mass

Women

Athletic: 14–20% body fat · 80–86% lean mass
Fitness: 21–24% body fat · 76–79% lean mass
Average: 25–31% body fat · 69–75% lean mass

LBM vs muscle mass vs FFMI vs Navy method

Muscle: Muscle mass ≈ subset of LBM. Roughly 40–50% of LBM is skeletal muscle in healthy adults—the rest is water, bone, organs.
FFMI: FFMI (fat-free mass index) normalizes LBM by height²—use our FFMI calculator after you have an LBM estimate.
Navy tape: U.S. Navy tape formulas measure body fat directly from circumferences—often closer to “true” BF% for trained users who measure consistently.

Limitations of formula-based LBM

•Formulas estimate LBM from height and weight only—age is collected for context but does not change Boer/James/Hume math here
•Typical error vs DEXA is often ±3–5 percentage points of body fat; athletes and very lean individuals may see larger gaps
•LBM includes water, bone, and organs—not the same as skeletal muscle mass alone
•Not for pregnancy, edema, amputation, or clinical malnutrition without professional assessment
•Implied body fat % is derived from formula output, not measured with calipers or scans

Worked example

Male, 70 kg, 175 cm — Boer formula

Default demo values

(0.407×70) + (0.267×175) − 19.2 = 56.02 kg

Lean body weight: 56.02 kg · Fat mass: 13.99 kg (20%)

Lean mass: 80% · BMI: 22.9 (Normal weight)

James on same inputs: 56.52 kg LBM · Hume: 52.81 kg LBM

References

Boer P. (1984) — Estimated lean body mass from height and weight regressionWidely used clinical estimate referenced in nutrition texts.
CDC — BMI for adults (context alongside LBM)
ACE body composition guidelinesFitness body fat category teaching ranges cited on this page.

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Body composition

Lean Body Weight Calculator

Last updated: June 4, 2026

Boer, James & Hume with live comparison

Implied body fat % and ACE-style range context

Step-by-step formula display in results

Lean body weight calculator

Boer, James, or Hume LBM with implied body fat % — educational, not DEXA

Weight (kg)

Height (cm)

Sex (formula)

Age (years)

Formula

Results

Boer (1984) — common clinical estimate

Lean body weight

56.02 kg

Implied body fat

20%

(0.407×70) + (0.267×175) − 19.2 = 56.02 kg

Fat mass

13.99 kg

Lean %

80%

BMI

22.9 (Normal weight)

Ideal LBW (teaching)

56.85 kg

Compare formulas

Boer (1984) 56.02 kg · 20% BF

James (1976) 56.52 kg · 19.3% BF

Hume (1966) 52.81 kg · 24.6% BF

Solid fitness range—progressive overload 2–4×/week.

DEXA, BodPod, or calipers measure composition more directly—formulas are estimates.

Estimates only. Regression LBM is not DEXA. Athletes, pregnancy, edema, and clinical illness need professional body composition assessment—not formula body fat alone.

Example results (from calculator logic)

Male 70 kg · 175 cm · Boer

56.02 kg LBM

~20% implied fat · BMI 22.9

Female 65 kg · 165 cm

46.13 kg LBM

~29% implied fat

Male 75 kg · 175 cm

58.05 kg LBM

~22.6% implied fat

LBM formulas (equations)

Formula	Male	Female
Boer (1984)	LBM = 0.407×weight(kg) + 0.267×height(cm) − 19.2	LBM = 0.252×weight(kg) + 0.473×height(cm) − 48.3
James (1976)	LBM = 1.10×weight − 128×(weight/height)²	LBM = 1.07×weight − 148×(weight/height)²
Hume (1966)	LBM = 0.3281×weight + 0.33929×height − 29.5336	LBM = 0.29569×weight + 0.41813×height − 43.2933

Implied body fat % = (weight − LBM) ÷ weight × 100

ACE-style body fat & lean mass ranges (teaching)

Men

Athletic: 6–13% body fat · 87–94% lean mass
Fitness: 14–17% body fat · 83–86% lean mass
Average: 18–24% body fat · 76–82% lean mass

Women

Athletic: 14–20% body fat · 80–86% lean mass
Fitness: 21–24% body fat · 76–79% lean mass
Average: 25–31% body fat · 69–75% lean mass

LBM vs muscle mass vs FFMI vs Navy method

Muscle: Muscle mass ≈ subset of LBM. Roughly 40–50% of LBM is skeletal muscle in healthy adults—the rest is water, bone, organs.
FFMI: FFMI (fat-free mass index) normalizes LBM by height²—use our FFMI calculator after you have an LBM estimate.
Navy tape: U.S. Navy tape formulas measure body fat directly from circumferences—often closer to “true” BF% for trained users who measure consistently.

Limitations of formula-based LBM

•Formulas estimate LBM from height and weight only—age is collected for context but does not change Boer/James/Hume math here
•Typical error vs DEXA is often ±3–5 percentage points of body fat; athletes and very lean individuals may see larger gaps
•LBM includes water, bone, and organs—not the same as skeletal muscle mass alone
•Not for pregnancy, edema, amputation, or clinical malnutrition without professional assessment
•Implied body fat % is derived from formula output, not measured with calipers or scans

Worked example

Male, 70 kg, 175 cm — Boer formula

Default demo values

(0.407×70) + (0.267×175) − 19.2 = 56.02 kg

Lean body weight: 56.02 kg · Fat mass: 13.99 kg (20%)

Lean mass: 80% · BMI: 22.9 (Normal weight)

James on same inputs: 56.52 kg LBM · Hume: 52.81 kg LBM

References

Boer P. (1984) — Estimated lean body mass from height and weight regressionWidely used clinical estimate referenced in nutrition texts.
CDC — BMI for adults (context alongside LBM)
ACE body composition guidelinesFitness body fat category teaching ranges cited on this page.