Lean Body Mass Calculator - Boer, James, and Hume

A lean body mass calculator on this site estimates adult LBM in kilograms from current weight W (kg), standing height H (cm), and sex. Three named regressions always run: Boer, James, and Hume. They disagree with each other because they were fitted on different samples with different laboratory references. None of them is a DEXA scan, a Bod Pod, or a diagnosis of sarcopenia or obesity.

The default male inputs are 80 kg and 180 cm. Boer men: 0.407W + 0.267H − 19.2 = 0.407×80 + 0.267×180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg. That identity is the implementation check. James and Hume return other kilograms for the same person; both are shown so you are not tricked into thinking there is one “true” LBM from height and weight.

Sex is required. Male and female coefficients are not interchangeable. Imperial pounds and feet-inches are converted to kg and cm before the formulas. James uses (W/H)² with H in centimetres, not metres - using metres would explode the square term.

Optionally, if you type a body-fat percentage, a fourth line is LBM = W × (1 − BF/100), labeled “from body-fat %”. That line is not Boer. A Navy tape BF% from the body fat calculator will not match Boer, because tape adiposity and height–weight LBM are independent methods.

Lean body mass is not identical to fat-free mass in every textbook, and neither is skeletal muscle. Organs, bone, and water dominate LBM. Do not treat 61.42 kg as “61 kg of muscle.” For kg/m² screening use the BMI calculator. For m² of estimated skin, use the body surface area calculator.

1. Choose male or female. Coefficients change.
2. Choose metric (cm, kg) or imperial (ft/in, lb). Formulas run in kg and cm.
3. Enter standing height and a recent weight. Read Boer, James, and Hume. Optionally add BF% for the independent W×(1−BF/100) check.
4. Copy if you need a record. Inputs stay in this browser up to 30 days and are never uploaded. These are screening equations, not a prescription.

Default male: W = 80, H = 180. Boer = 61.42 kg exactly on these coefficients. James men: 1.1×80 − 128×(80/180)² = 88 − 128×(16/81) = 88 − 128×0.197530864 ≈ 62.72 kg. Hume men: 0.32810×80 + 0.33929×180 − 29.5336 = 26.248 + 61.0722 − 29.5336 = 57.79 kg. Three answers, one body: that spread is the lesson.

Female illustration at the same size (not a recommendation): Boer women 0.252×80 + 0.473×180 − 48.3 = 20.16 + 85.14 − 48.3 = 56.99 kg. James and Hume will differ again. Do not average the three and call it science unless a protocol you follow says to; this page reports them separately.

If BF% = 20 is entered at 80 kg, the optional line is 80 × 0.80 = 64 kg from body-fat %, which is not Boer (61.42 kg). The mismatch is expected. Pick the method that matches the question; do not launder a tape percentage through Boer.

These equations show up in clinical literature when someone needs an LBM or FFM estimate and only height, weight, and sex are on the chart. Boer (1984) is often cited in that setting. James appears in older ICU and nutrition papers. Hume (with Weyers) published anthropometric lean-mass estimates in the early 1970s. A website reproducing the algebra is not a substitute for the paper, the assay, or the patient in front of you.

Some kidney and drug-dosing discussions use LBM or ideal body weight as an input. This page will not compute a creatinine clearance, an eGFR, or a milligram dose. Ideal weight formulas (Devine, Robinson, Miller, Hamwi) are a different family on the ideal weight calculator. Mixing IBW and Boer LBM as if they were synonyms is a common spreadsheet error.

Hypertrophy and very low fat mass sit outside the samples. A 180 cm, 110 kg powerlifter can have more lean tissue than Boer predicts from an “average” 80 kg adult of that height. An older adult at 80 kg may have less muscle and more visceral fat than Boer implies. Katch–McArdle BMR needs an LBM input; if you go that way, know which LBM you fed the BMR calculator.

Children, pregnancy, amputation, severe edema, and critical illness are out of scope. Pediatric LBM is not adult Boer with a shorter H. Gestational weight is not “LBM plus a baby” in these coefficients. This tool will still do arithmetic on odd inputs within range checks, but the labels remain adult population equations.

BMI is mass / height². LBM is an estimated leftover after imagined fat. You can have a “normal” BMI and a modest Boer LBM, or a high BMI with high LBM. The overweight calculator and underweight BMI calculator stay in the WHO kg/m² world. This page does not.

Protein rules of thumb sometimes use g/kg of LBM instead of g/kg of total mass. That is a planning choice, not a lab result. Estimate grams on the protein calculator and splits on the macro calculator. Army or Navy tape percentages belong on their own calculators, including the Army body fat calculator.

Search still asks “how to calculate lean body mass,” “Boer formula,” and “LBM 80 kg 180 cm.” The answers: use a named equation and report which one; Boer men is 0.407W+0.267H−19.2; 61.42 kg is the default check. Anything about winning a sport or treating disease is outside this form.

Extra male Boer checks: 70 kg / 170 cm → 0.407×70 + 0.267×170 − 19.2 = 28.49 + 45.39 − 19.2 = 54.68 kg. 90 kg / 190 cm → 36.63 + 50.73 − 19.2 = 68.16 kg. 60 kg / 160 cm → 24.42 + 42.72 − 19.2 = 47.94 kg. James and Hume will not copy those kilograms. That is the point of showing all three.

Stigma applies here too. “Not enough lean mass” as a self-attack is not what these regressions are for. If weight or food thoughts dominate your day, contact a clinician. LBM formulas cannot diagnose an eating disorder or prescribe a training block. Calories burned in a session are a different estimate on the calories burned calculator.

Metric is the native language of Boer, James, and Hume. Imperial is a courtesy conversion. 180 cm is 70.866 inches, not a clean 5 ft 11 in (71 in = 180.34 cm). The default imperial fields (5 ft 11 in, 176 lb) are nearby, not identical to 80 kg / 180 cm. If you need the 61.42 kg Boer check, stay on metric 80 / 180. Switching units without converting the numbers is how people “break” the default and think the site is wrong.

Female Boer at 65 kg and 165 cm: 0.252×65 + 0.473×165 − 48.3 = 16.38 + 78.045 − 48.3 = 46.125 kg. James women: 1.07×65 − 148×(65/165)² = 69.55 − 148×0.155188 ≈ 46.58 kg. Hume women: 0.29569×65 + 0.41813×165 − 43.2933 = 19.220 + 68.991 − 43.293 ≈ 44.92 kg. Again the trio disagrees. Report the name of the equation if you write the kilogram down. “My LBM is 46” without “Boer” is how numbers wander into the wrong spreadsheet column.

James pitfalls: H must be centimetres. If someone copies a blog that used metres, (W/H)² becomes huge and LBM goes negative or absurd. This page guards with a non-physical check, but the real fix is units. James also punishes a high W/H ratio (stocky or high-BMI bodies) more aggressively than Boer because of the squared term. That is a property of the curve, not a moral judgment about “too much weight for height.”

Hume’s extra decimal places (0.32810, 0.33929, 29.5336) look like false precision. They are the published coefficients; changing them to two decimals would be a different formula. We keep the digits. The result is still an estimate with kilogram-scale uncertainty versus a scan.

Using LBM in TDEE: some people feed LBM into Katch–McArdle BMR. If you do, use one named LBM and do not average Boer and Hume “to be safe” unless you document that average as your own invention. The BMR calculator and calorie calculator are still planning tools. A 61.42 kg Boer number does not entitle anyone to a specific calorie budget.

Optional BF% line: suppose 80 kg and a Navy tape of 13.36%. W × (1 − 0.1336) = 69.31 kg “from body-fat %.” Boer was 61.42 kg. Those 8 kg of disagreement are the cost of mixing methods. Athletes with extra muscle often look “too heavy” for Boer and “reasonably lean” on a tape, or the reverse. Pick a method for a time series and stick to it. For the tape itself, use the body fat calculator; do not paste a made-up BF% to force Boer to match.

What these equations omit: bone mineral density, limb length ratios, ascites, casts, and whether the 80 kg is glycogen and water after a carb load. A 2 kg overnight swing is mostly water, not a 2 kg lean-mass miracle. Week-to-week LBM from Boer only moves when height or weight or the sex toggle moves - height should not move much in adults - so “Boer LBM tracking” is mostly weight tracking with extra arithmetic.

Children need pediatric FFM methods. Pregnancy is not “female Boer plus fetus.” Amputation requires adjusted mass estimates from rehabilitation literature, not a shorter height stuffed into Hume. This page’s range checks stop some nonsense but not all clinical contraindication. When the body is not a textbook cylinder, skip the web form.

Hume versus Boer on the default male is a 3.6 kg gap (61.42 vs 57.79). That gap is larger than many people expect from “just another LBM formula.” If a paper specifies Hume, using Boer because it is the big number on this page is a citation error. If a coach specifies nothing, showing all three and picking none for a prescription is the honest move.

Fat mass implied by Boer is weight minus Boer LBM: 80 − 61.42 = 18.58 kg, or about 23.2% if you naively divide by weight. That implied percentage is not a Navy tape and not DEXA. Do not cross-check it against the body fat calculator and declare one of them broken. They measure different constructs with different errors.

Sex toggles coefficients; they do not encode gender- affirming care, intersex variation, or hormone status. Population equations were built on binary samples. If those samples do not describe you, these kilograms are even less applicable. That limitation is a reason to prefer a clinical composition method, not a reason for this page to invent a third sex coefficient.

Storage key lean-body-mass-calculator-data is unique. Optional BF% is stored with the rest for 30 days on this device only. Clear empties BF% too. The split class lean-body-mass-split-track isolates desktop resize. Copy includes the three names so a paste cannot collapse into a single unlabeled kilogram.

Protein and calorie tools still need a goal you choose, not a Boer kilogram that chooses it for you. Pair this page with the protein calculator only as a planning sketch. The 61.42 kg default is an arithmetic identity, not a hypertrophy target and not a clinical FFM from a scan.

Repeat the 61.42 kg check after a browser refresh: male, metric, 80 kg, 180 cm, Boer must still print 61.42. If it does not, the page is broken, not your body. James and Hume should remain near 62.72 kg and 57.79 kg on that same default. Leave the optional body-fat box empty for that audit so a fourth line does not distract from the three named regressions.