Composition from height and weight

Lean Body Mass Calculator: LBM from Boer, James, and Hume

This calculator estimates lean body mass (LBM), the weight excluding storage fat, from height, weight, and sex. Adults get the mean of Boer, James, and Hume; cohort ≤14 uses Peters. It reports body fat %, functional mass ratio, a composition bar, and a model comparison table. Optional manual body fat % updates the fat readout and bar. Educational only; not for medication dosing.

By Jeff Beem

Updated September 24, 2026

Inputs

Units

Cohort

Pediatric mode switches to the Peters estimate.

Sex

Height

Weight

Manual body fat % (optional)

Leave blank for the formula-derived estimate.

Results

Body fat %

23.3%

From LBM vs weight.

Functional mass ratio

76.7%

Composition

Lean 53.7 kgFat 16.3 kg

Model comparison

Lean body mass and body fat percent by formula
Formula	Use	LBM	BF%
Boer	Standard clinical	54.7 kg	21.9%
James	Non-obese profiles	55.3 kg	21.0%
Hume	Broad population	51.1 kg	27.0%

How to use this calculator

Begin at the top of the form. Choose metric or US units, pick whether you want the adult formulas or the pediatric Peters option, then enter sex, height, and weight.

If you already know your body fat percent from a scan or calipers, you can type it in the optional field. That only changes the body-fat card and the lean-versus-fat bar. The main lean body mass number still comes from height and weight.

When you are ready, look at section 02. The dark card is your estimated lean body mass. Under it you will see body fat percent, how much of your total weight that lean mass represents, a simple lean-versus-fat bar, and (for adults) a small table that shows what each formula would say on its own. Treat these numbers as a learning estimate, not a lab report or a dosing guide.

Reading your lean body mass result

Start with the dark panel: that is your headline lean body mass (LBM). The white cards under it explain body fat %, how much of your weight is lean (functional mass ratio), the lean-vs-fat bar, and, for adults, each formula on its own.

Example: male, 170 cm, 70 kg (metric defaults)

By default the form uses a male adult at 170 cm and 70 kg. Headline LBM is about 53.7 kg (118.4 lb), body fat about 23.3%, and functional mass ratio about 76.7%. The model table shows Boer near 54.7 kg, James 55.3 kg, and Hume 51.1 kg, each with its own body-fat column. The composition bar mirrors the headline: about 53.7 kg lean and 16.3 kg fat.

Example: pediatric cohort ≤14 (Peters)

Keep the same height and weight, then switch cohort to ≤14 (Peters). The adult comparison table disappears and Peters alone estimates LBM near 52.5 kg. Body fat % is still 100 − (LBM ÷ weight × 100), now based on that Peters value instead of the adult mean.

Manual body fat % vs headline LBM

A measured body fat % from dual-energy X-ray absorptiometry (DEXA), calipers, or a similar method only drives the body-fat card and composition bar. Headline LBM and functional mass ratio stay on the Boer/James/Hume mean (or Peters) until you change height, weight, sex, or cohort. That split keeps the anthropometric estimate visible even when you have a better fat measurement.

Lean body mass calculator: Boer, James, Hume, and Peters

This calculator estimates lean body mass (LBM) from height, weight, and sex. Adults use the mean of Boer, James, and Hume; cohort ≤14 uses Peters. Optional manual body fat % updates the fat readout and bar only. Educational only; not medical or dosing advice.

What this calculator does

The widget estimates lean body mass (LBM), the part of your weight that is not storage fat, from height, weight, and sex. Cohort Adult averages Boer, James, and Hume. Cohort ≤14 (Peters) uses the pediatric estimate and hides the adult table. Body fat % defaults to 100 − (LBM ÷ weight × 100). If you enter a manual body fat %, that value updates only the body-fat card and composition bar; headline LBM and functional mass ratio stay formula-based. The page does not run imaging, set protein targets, or replace a clinical test.

Boer (male, W kg, H cm):

$\mathrm{LBM}=0.407W+0.267H-19.2$
James (male):

$\mathrm{LBM}=1.1W-128\,(W/H)^2$
Hume (male):

$\mathrm{LBM}=0.32810W+0.33929H-29.5336$
Peters (pediatric):

$e\mathrm{LBM}=3.8\times(0.0215\,W^{0.6469}\,H^{0.7236})$

LBM vs fat-free mass (FFM)

Lean body mass (LBM) still counts a little essential fat in organs and nerves. Fat-free mass (FFM) excludes essentially all lipid (often about 2–3% of weight in men and 5–12% in women). This page labels results as LBM on the dark panel and in the comparison table, so you are not mixing the two definitions by accident.

Accuracy and limits

Height-and-weight formulas are population averages. They can miss unusual muscle, low muscle in older adults, or obesity (James especially). At a default male of 70 kg and 170 cm, the three adult models already span about 4 kg; the mean summarizes that range, it is not a measured lean mass. Manual body fat % improves the fat side of the composition bar when you have DEXA or field data; it does not rewrite headline LBM. Do not use this page for medication dosing. Basal metabolic rate (BMR) and total daily energy expenditure (TDEE) live on their own calculators.

FAQ

How is the headline LBM calculated for adults?

With cohort Adult, the dark results card averages three classic height-and-weight formulas: Boer, James, and Hume. Each one uses your weight in kilograms, height in centimeters, and sex-specific coefficients. Body fat % on the card is 100 − (LBM ÷ weight × 100) from that headline value, unless you type a manual body fat %. The Model comparison table still lists each formula on its own, with its own implied body fat %.

What lean body mass do the metric defaults show?

The calculator defaults to a male at 170 cm and 70 kg on cohort Adult. Headline lean body mass (LBM) lands near 53.7 kg (about 118.4 lb), body fat near 23.3%, and functional mass ratio near 76.7%. In the comparison table, Boer is about 54.7 kg, James 55.3 kg, and Hume 51.1 kg. The composition bar splits that into roughly 53.7 kg lean and 16.3 kg fat.

When does the widget use the Peters formula?

Switch cohort to ≤14 (Peters). Pediatric mode hides the adult comparison table and uses Peters only:

e\mathrm{LBM}=3.8\times(0.0215\,W^{0.6469}\,H^{0.7236})

where W is weight in kg and H is height in cm. Sex still selects the coefficients the equation needs. Keep Adult selected for anyone past that pediatric cohort.

What does manual body fat % change?

If you enter a measured body fat %, that number replaces the formula-derived body fat readout and rebuilds the composition bar (lean and fat mass from your total weight). The dark-panel headline LBM and the functional mass ratio still come from the formula mean (or Peters). Leave the field blank when you want body fat % derived from the LBM estimate.

What is functional mass ratio?

It is (headline LBM ÷ weight) × 100, the lean share of your scale weight. At the defaults it reads about 76.7%, which matches 100% − 23.3% body fat because both come from the same formula LBM. If you turn on manual body fat %, the body-fat card follows your entry while functional mass ratio still tracks the formula headline.

Which formula is most accurate: Boer, James, or Hume?

None fits every build. Boer is the usual clinical default. James works for many non-obese adults but can skew with obesity. Hume is a broad linear baseline. At the defaults the three span about 4 kg (54.7 down to 51.1). This page averages them for the headline instead of pretending one winner fits everyone.

Can I use this for medication dosing?

No. Some hospital protocols reference lean mass or adjusted body weight, but this page is educational only. It does not replace a prescribing clinician or your institution’s dosing rules.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]

Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632-F636

Boer formula for lean body mass estimation, used as the standard clinical LBM calculation method.

[2]

Janmahasatian S, Duffull SB, Ash S, et al. Quantification of lean bodyweight. Clin Pharmacokinet. 2005;44(10):1051-1065

Pharmacokinetic modeling paper on predicting fat-free mass / lean bodyweight from sex, height, and weight; cites James W. (Research on Obesity, HMSO 1976) and situates classic anthropometric LBM estimates used in clinical dosing alongside newer approaches.

[3]

Hume R. Prediction of lean body mass from height and weight. J Clin Pathol. 1966;19(4):389-391

Hume linear LBM formula using height and weight, providing a broad population baseline for lean mass estimation.

Fitness Reference Note

Informational Use: These calculations (BMI, Calories, etc.) are based on standard statistical formulas and are intended for general reference and goal-setting purposes only.

Consult Experts: This tool does not provide medical advice, diagnosis, or treatment. Results may not be accurate for athletes, pregnant individuals, or those with underlying health conditions.

Health Safety: Always consult with a healthcare professional or qualified trainer before beginning any new diet or intensive exercise program.

Privacy First: All calculations are performed locally in your browser. No health data is stored or transmitted to any server.