Lean Body Mass Calculator

Formula	LBM (kg)	LBM (lb)	Body Fat (%)	Copy
{{ row.label }}	{{ format(row.lbmKg) }}	{{ format(row.lbmLb) }}	{{ row.fatPercent.toFixed(1) }}

Use a lean body mass calculator online to estimate your fat‑free mass. You convert everyday measurements into a practical indicator of body composition. The concept is Lean Body Mass (LBM), a common synonym is fat‑free mass, and the abbreviation appears frequently in training, nutrition, and pharmacokinetics.

The tool computes LBM from your numbers and returns values in familiar weight units, along with an inferred fat fraction. Inputs are numeric entries such as body weight, stature, and optional tape measurements, plus one categorical choice for biological sex. Outputs help you compare methods and discuss trends with coaches or clinicians.

For example, you might enter moderate weight and average height to see how medical equations differ by a few kilograms, then use one consistently to track change. Interpret results alongside context such as hydration, device tolerance, and measurement repeatability. This tool provides informational estimates and does not substitute professional advice.

Technical Details:

Lean body mass is modeled as total body mass minus adipose tissue, expressed in kilograms and optionally pounds. Implemented methods include Boer, James, Hume, and Janmahasatian equations; optional body‑fat percent (BF%) can be derived from Deurenberg or U.S. Navy tape formulas to construct an alternate lean‑mass estimate. Coefficients, units, conversions, and rounding match the implementation described below.

\begin{array}{lcl} LBM : Boer (male) & = & 0.407 W + 0.267 H - 19.2 \\ LBM : Boer (female) & = & 0.252 W + 0.473 H - 48.3 \\ LBM : James (male) & = & 1.10 W - 128 \frac{W^{2}}{H^{2}} \\ LBM : James (female) & = & 1.07 W - 148 \frac{W^{2}}{H^{2}} \\ LBM : Hume (male) & = & 0.32810 W + 0.33929 H - 29.5336 \\ LBM : Hume (female) & = & 0.29569 W + 0.41813 H - 43.2933 \\ LBM : Janmahasatian & = & \frac{9270 W}{6680 + 216 \cdot BMI} \end{array}

Here, W is weight in kilograms and H is height in centimetres; BMI is body mass index with height in metres: BMI = W/(H/100) 2. The Janmahasatian implementation above uses a single coefficient set regardless of sex as coded.

Symbols and units used by the equations

Symbol	Meaning	Unit/Datatype	Source
LBM	Lean body mass	kg	Derived
W	Body weight	kg	Input (kg or lb → kg)
H	Stature height	cm	Input (cm or in → cm)
BMI	Body mass index	kg/m²	Derived
s	Sex indicator (male‑1, female‑0)	dimensionless	Input (for BF% only)
a	Age for Deurenberg BF% model	years	Input

Optional BF% estimators feeding an alternate lean‑mass row:

\begin{array}{lcl} BF % : Deurenberg & = & 1.2 BMI + 0.23 a - 10.8 s - 5.4 \\ BF % : U.S. Navy (male) & = & 86.010 \log_{10} (waist - neck) - 70.041 \log_{10} (height) + 36.76 \\ BF % : U.S. Navy (female) & = & 163.205 \log_{10} (waist + hip - neck) - 97.684 \log_{10} (height) - 78.387 \end{array}

If a BF% value p is available, an alternate lean mass is computed as LBM_alt = W × (1 − p/100) with clamping to 0–70%.

Interpretation and bounds

Threshold Band	Lower Bound	Upper Bound	Interpretation	Action Cue
BF% clamp range	0	70	Code limits BF% for alternate row; not a clinical threshold.	Re‑measure if near 0% or > 60%.
LBM (all formulas)	—	—	Continuous estimate; no categorical bands are applied.	Track change over time with one chosen method.

No categorical labels are assigned by the calculator; interpretation depends on context and consistency of method across measurements.

Parameters accepted by the calculator

Parameter	Meaning	Unit/Datatype	Typical Range	Sensitivity	Notes
Weight	Body mass	kg or lb	Adult ~40–180	High	Converted via 1 lb = 0.45359237 kg.
Height	Stature without shoes	cm or in	Adult ~140–210	High	Converted via 1 in = 2.54 cm.
Sex	Male or female	categorical	—	Medium	Affects Boer, James, Hume; Janma variant here is sex‑agnostic.
BF% (known)	Direct body‑fat percent	percent	Typically 3–60	High	Clamped 0–70% in code when used.
Age	Age in years (Deurenberg)	integer	Adult ~18–80	Medium	Used only for Deurenberg BF%.
Waist/Neck/Hip	Circumferences (tape)	cm or in	Varies	Medium	Required for U.S. Navy method; unit toggle available.

Units, precision, and rounding policy

Item	Policy	Detail
Decimal separator	Locale‑aware formatting	Uses browser locale via toLocaleString.
Mass outputs	Fixed decimals	LBM kg/lb and fat kg rounded to 2 decimals.
Body‑fat percent	Displayed precision	Table/badges show 1 decimal; internal value is full precision.
Rounding ties	Nearest, half away from zero	JavaScript number formatting behavior.
Unit conversions	Exact constants	1 lb=0.45359237 kg; 1 in=2.54 cm; 1 kg=2.20462262 lb.
Logarithm base	U.S. Navy method	Base‑10 log for tape equations.

Validation and bounds extracted from code

Field	Type	Min	Max	Step/Pattern	Error Text
Weight	number	0	—	0.1	None; results hidden if invalid.
Height	number	0	—	0.1	None; results hidden if invalid.
Sex	radio	—	—	male\|female	—
Formula	select	—	—	Boer\|James\|Hume\|Janmahasatian	—
Known BF%	number	0	60	0.1; code clamps 0–70%	No explicit error; ignored if 0.
Age	number	0	120	1	—
Waist/Neck/Hip	number	0	—	0.1; male requires waist>neck; female requires waist+hip>neck	No explicit error; BF% not shown if invalid.

Worked example

Inputs: weight 82 kg, height 178 cm, sex male. Using Boer:

\begin{array}{lcl} LBM & = & 0.407 \times 82 + 0.267 \times 178 - 19.2 \\ LBM & = & 61.70 kg (rounded to 2 decimals) \\ Fat & = & 82 - 61.70 = 20.30 kg \\ BF % & = & \frac{20.30}{82} \times 100 = 24.8 % (display) \end{array}

Optional Deurenberg (age 35): BF% ≈ 22.9% → alternate LBM ≈ 63.22 kg after clamping.

Assumes adult anthropometry; pediatric or extreme cases may deviate.
Heads‑up Janmahasatian variant here does not switch coefficients by sex.
Derived BF% used for the alternate row is clamped to 0–70%; this is not a diagnosis.
Heads‑up Locale formatting and binary floating‑point can create tiny rounding quirks.
Charts are cosmetic and do not affect numeric results.

Zero or negative inputs yield no results until corrected.
U.S. Navy male tape requires waist > neck; otherwise no BF% appears.
U.S. Navy female tape requires waist + hip > neck; otherwise no BF% appears.
Height entered in inches is converted to centimetres before all equations.
Copy/CSV/JSON rely on clipboard and download features; browser policies may interfere.

Scientific/Standards Backing — Equations originate from peer‑reviewed sources including Boer, James, and Hume lean‑mass models; Janmahasatian et al. pharmacokinetic dosing research; Deurenberg BF% regression; and U.S. Navy circumference equations.

Privacy & Compliance — Calculations and formatting run in your browser; no fetch/XHR calls send your inputs to a server. Clipboard and downloads act locally; health data is sensitive, so handle outputs accordingly.

Step‑by‑Step Guide:

Follow these steps to compute and compare lean mass.

Enter Weight and choose kg or lb.
Enter Height and choose cm or in.
Select Sex for equations that require it.
Pick a Formula to highlight in the results.
Open Advanced and choose a body‑fat method if you want an alternate lean‑mass row.
For U.S. Navy measure waist/neck (and hip for females) consistently at the specified landmarks.

Example: 72 kg, 170 cm, female, Boer → LBM ≈ 49–51 kg depending on method spread; add age 30 in Deurenberg for an alternate BF% and lean mass.

Use the JSON view to capture inputs and outputs together.
Use CSV to compare methods side by side in external analysis.

FAQ:

Is my data stored?

No. Inputs are processed client‑side only; there are no fetch/XHR calls to servers. Copy and download actions operate locally in your browser.

How accurate are the formulas?

They are validated estimators with known biases by population and method. Use one consistently for tracking rather than mixing. The Janmahasatian variant here does not change by sex, which may affect individual accuracy.

What units and formats are supported?

Weight accepts kg or lb; height accepts cm or in; tape measures accept cm or in. Results show 2 decimals for masses and 1 decimal for displayed BF%. JSON contains numeric values.

Can I use it offline?

Once loaded in your browser, calculations do not require connectivity. There are no network requests during computation.

Why is my U.S. Navy BF% blank?

For males, waist must exceed neck; for females, waist plus hip must exceed neck. All required fields must be positive. If conditions are not met, the app omits the alternate BF% row.

What does LBM stand for?

Lean Body Mass, also called fat‑free mass. It represents body mass minus adipose tissue and is expressed in kilograms or pounds.

Do I need a license or API key?

No API endpoints or keys are used; calculations run locally in the UI layer. Use outputs freely; check site terms for any additional conditions.

Troubleshooting:

Result area is empty: ensure weight and height are positive and realistic.
Alternate BF% missing: verify U.S. Navy inequalities and required measurements.
Copy fails: grant clipboard permission or use download instead.
Numbers show commas or spaces: this follows your locale’s decimal separator.
Charts not visible: switch tabs back and forth or resize the window to trigger redraw.

No output appears after entry — check for negative or zero inputs; the calculator suppresses results if any core value fails validation.

Glossary:

Lean Body Mass (LBM): Body mass minus fat mass; expressed in kilograms or pounds.
Body Fat Percent (BF%): Proportion of body mass composed of adipose tissue.
Body Mass Index (BMI): Weight divided by height squared with height in metres.
Deurenberg equation: Regression linking BMI, age, and sex to BF%.
U.S. Navy method: Tape‑measure BF% using waist, neck, and hip equations.
Janmahasatian formula: Lean‑mass model using BMI in the denominator.
Rounding policy: Masses to two decimals; BF% display to one decimal.

Tool name and category from metadata.