Lean Body Mass Calculator

Formula	LBM (kg)	LBM (lb)	Body Fat (%)	Copy
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Lean body mass is the share of weight that is not fat. It reflects muscle bone organs and body water and helps you read composition rather than scale weight alone.

People use it to set training goals and to frame health conversations. Many look for a lean body mass calculator using Boer James Hume and Janmahasatian so they can compare results across familiar methods.

Enter weight and height then pick sex and choose a method. You see lean mass in kilograms and pounds along with the implied fat share. Checking several methods side by side shows how stable the estimate is.

If you already know body fat percent you can cross check by entering it or by estimating with age and body size or by the US Navy tape approach using waist neck and hip. Consistent measuring and the same units across runs give steadier trends.

Results are estimates so treat edges with care. Body shapes vary and athletes and older adults can sit off the usual pattern. This tool provides informational estimates and does not substitute professional advice.

Technical Details:

Lean body mass (LBM) represents the portion of body mass free of adipose tissue. It is inferred from body mass and stature measured at a point in time for an adult and summarized in kilograms and pounds.

Each method transforms weight and height into an LBM estimate with coefficients that differ by method and by sex when applicable. Interpreting LBM focuses on the absolute kilograms of lean tissue and the complementary fat mass and percentage derived from total mass.

Close agreement across methods indicates a stable estimate for the given inputs. Wide spread suggests measurement noise or a body type that sits outside the typical populations used to derive the equations; treat such results cautiously and track trends rather than single values.

Comparisons are most meaningful within the same person over time under similar conditions. Values for children pregnant individuals and people with unusual fluid balance are outside scope.

Core equations (first method shown):

{LBM}_{Boer male} = 0.407 \times w + 0.267 \times h - 19.2

{LBM}_{Boer female} = 0.252 \times w + 0.473 \times h - 48.3

Symbols and units used in formulas
Symbol	Meaning	Unit/Datatype	Source
LBM	Lean body mass	kg	Derived
w	Body mass on the scale	kg	Input
h	Stature without shoes	cm	Input
BMI	Body mass index (w/(h/100)²)	kg/m²	Derived
a	Age	years	Input
s	Sex flag male=1 female=0	number	Input
W, N, H	Waist Neck Hip circumferences US Navy method	in	Input

Worked Example

Inputs: w=70 kg, h=175 cm, male using Boer.

\begin{array}{l} {LBM}_{Boer male} = 0.407 \times 70 + 0.267 \times 175 - 19.2 \\ = 56.015 kg \\ \approx 56.02 kg \end{array}

\begin{array}{l} Fat = w - LBM = 70 - 56.015 = 13.985 kg \\ \approx 13.99 kg \\ %BF = 100 \times \frac{Fat}{w} = 100 \times \frac{13.985}{70} \approx 20.0 % \end{array}

Interpretation: about 56.02 kg lean mass and about 20.0% fat for these inputs.

Other equations:

{LBM}_{James male} = 1.1 \times w - \frac{128 \times w^{2}}{h^{2}}

{LBM}_{James female} = 1.07 \times w - \frac{148 \times w^{2}}{h^{2}}

{LBM}_{Hume male} = 0.3281 \times w + 0.33929 \times h - 29.5336

{LBM}_{Hume female} = 0.29569 \times w + 0.41813 \times h - 43.2933

{LBM}_{Janmahasatian} = \frac{9270 \times w}{6680 + 216 \times BMI}

Optional body fat estimators:

%BF = 1.2 \times BMI + 0.23 \times a - 10.8 \times s - 5.4 (Deurenberg)

%BF = 86.01 \times {log}_{10} (W - N) - 70.041 \times {log}_{10} (height in in) + 36.76 (US Navy male)

%BF = 163.205 \times {log}_{10} (W + H - N) - 97.684 \times {log}_{10} (height in in) - 78.387 (US Navy female)

Units, precision, and rounding:

Weight accepts kilograms and pounds; height accepts centimeters and inches; circumferences accept centimeters and inches.
Conversions use 1 lb = 0.45359237 kg and 1 in = 2.54 cm.
Lean and fat masses display with two decimals; body fat percentage displays with one decimal.
Rounding follows standard JavaScript toFixed behavior for the stated decimal places.
US Navy equations use base‑10 logarithms and operate on inches internally.

Validation and bounds:

Validation rules enforced by the tool
Field	Type	Max	Step/Pattern	Error Text
Weight	number	–	0.1	Enter a weight and height greater than 0.
Height	number	–	0.1	Enter a weight and height greater than 0.
Known body fat %	number	60	0.1	Ignored if 0; clamped to 0–70% internally.
Age (Deurenberg)	integer	120	1	Used only when Deurenberg is selected.
Waist, Neck, Hip (Navy)	number	–	0.1	Heads‑up Male requires waist > neck; female requires waist + hip > neck.

I/O and encoding notes:

Inputs and outputs
Input	Accepted Families	Output	Encoding/Precision	Rounding
Weight, Height, Sex, Method	Numeric values; sex as selection	LBM, fat mass, body fat %	Two decimals for masses; one decimal for %	JavaScript decimal rounding
Optional BF estimators	Known %, Age, Tape measures	Alternate LBM row based on %BF	% clamped to 0–70	N/A

Networking and storage behavior:

Processing is client‑only; no data is transmitted or stored server‑side. Copy and download actions occur locally via the clipboard and file save dialogs.

Assumptions and limitations:

Adult inputs are assumed; pediatric and pregnancy contexts are out of scope.
Extreme body mass index values can reduce reliability.
Highly muscular or very low body fat physiques may deviate from estimates.
Hydration changes shift weight without changing tissue proportions.
US Navy equations require valid log10 arguments in inches.
Heads‑up Alternate %BF values are clamped to 0–70%.
Small unit entry errors can move results more than method choice.
Comparisons across different measurement days should use the same routine and timing.

Edge cases and error sources:

Zero or negative weight/height prevents calculation.
NaN inputs from empty fields produce no results.
Very small height values inflate BMI and distort Janmahasatian.
US Navy male fails when waist ≤ neck; female fails when waist + hip ≤ neck.
Log10 of non‑positive values is undefined.
Rounding at two decimals can hide small method differences.
Mixed units across sessions hinder trend comparison.
Typing thousands separators causes parse failure; enter plain numbers.
Excess precision in entries is rounded on display.
Clipboard permissions may block copy actions on restricted devices.

Step‑by‑Step Guide:

Estimate lean body mass and an optional body fat percentage, then compare methods side by side.

Enter Weight and choose its unit.
Enter Height and choose its unit.
Select Sex.
Choose a method; start with Boer for a balanced estimate.
Optional: choose a body fat method and provide its inputs.
Review lean mass, fat mass, and percent; copy or download if needed.

Example: 70 kg, 175 cm, male, Boer → about 56.02 kg lean and about 20.0% fat.

Measure at the same time of day for consistency.
If values disagree widely, recheck units and tape placement.

Pro tip: average two or three steady readings rather than relying on a single pass.

FAQ:

Is my data stored?

No. Calculations run locally and no entries are sent to a server. Copy and download actions use local device features.

Privacy: nothing is uploaded during calculation.

How accurate are the methods?

They are empirical estimates. Agreement across methods is a good sign; large spread suggests measurement issues or an atypical build. Track trends over time.

Which units can I use?

Weight supports kg and lb; height supports cm and in; tape measures support cm and in. Internally the Navy equations use inches.

Can I use it without a connection?

The calculations themselves are local. Once the page is open, changing inputs does not require a connection.

What does a borderline result mean?

Values near your typical range call for context. Compare multiple methods and repeat under similar conditions to see direction rather than fixating on a number.

How do I use the US Navy method?

Measure waist at the navel, neck below the larynx, and for females hip at the widest point. Ensure inches or centimeters match your selection.

How do I copy results?

Use the copy actions to place a CSV row or a JSON summary on your clipboard. You can also download the same data as files.

Is there any licensing or cost?

No explicit licensing terms are included in the package. Use is provided as‑is for informational purposes.

Troubleshooting:

No result appears — enter weight and height greater than 0.
Navy method empty — check that waist is bigger than neck for males and waist plus hip is bigger than neck for females.
Percent looks clipped — alternate body fat is clamped to 0–70%.
Numbers look odd — confirm units and decimal points not commas.
Charts do not update — verify inputs are valid and not empty.
Copy fails — allow clipboard permissions or use download instead.

If every field is filled and results still do not show, reset optional body fat inputs and re‑enter weight and height.

Advanced Tips:

Tip Take measurements at the same time of day after similar meals for better comparability.

Tip Start with Boer and then check Hume and Janmahasatian to gauge spread.

Tip Re‑measure tape positions twice and average to reduce random error.

Tip Track lean mass trends monthly rather than day to day to smooth water shifts.

Tip Use the same unit set each session to avoid hidden conversion variation.

Tip When methods disagree, prefer the one you can reproduce most consistently.

Glossary:

Lean body mass (LBM): Body mass excluding fat tissue expressed in kilograms.
Body fat percentage (%BF): Fat mass divided by total mass as a percentage.
Body mass index (BMI): Weight divided by height squared expressed in kg/m².
Deurenberg: Formula estimating %BF from BMI age and sex.
US Navy method: Tape‑based %BF estimate using waist neck and hip.
Log10: Base‑10 logarithm used by the tape equations.
Clamping: Restricting a value to a safe range such as 0–70%.