What is lean body mass?
Lean body mass (LBM) is total body weight minus stored fat — it includes muscle, bone, organs, blood and water, not just skeletal muscle. This lean body mass calculator estimates LBM from sex, height and weight with the Boer/James/Hume formula set, shows lean body mass in kg and lbs, and can apply an optional body fat percentage method when you already know body fat and lean mass split from DEXA or bioimpedance.
Weight composition (concept)
Total weight ≈ lean body mass + fat mass. Boer estimates the lean share.
Typical LBM share by sex (teaching)
Not a diagnosis — illustrative ranges often cited in fitness texts.
How to calculate lean body mass
- Select female or male — all three anthropometric formulas are sex-specific.
- Measure height (cm or in) and weight (kg or lb) on the same day when possible.
- Apply the Boer formula (primary on this page) or compare James and Hume in the results panel.
- If you know body fat percentage, compute LBM = weight × (1 − BF/100) for a direct method.
- Report lean body mass in kg; multiply by 2.2046 for pounds if needed.
Lean body mass formulas (Boer, James, Hume)
The primary lean body mass calculator formula here is Boer (1984), commonly used in nutrition research and body-composition teaching. James (1976) and Hume (1966) are older regression equations — results may differ by 1–3 kg for the same person.
Boer formula (primary)
James formula
Hume formula
Body fat percentage method
When body fat percentage is measured (DEXA, BIA, calipers), LBM does not need height:
LBM with known body fat %
Enter BF% in the calculator to see this value next to Boer. Large gaps suggest the anthropometric estimate does not match your measurement method — trust the direct BF% path for that dataset.
Lean body mass for men and women
A lean body mass calculator for men uses higher typical lean fractions and different Boer intercepts than a lean body mass calculator for women. Sex hormones, height and weight distribution change the estimated lean body mass percentage of total weight. Always select sex before interpreting LBM % teaching ranges.
kg, lbs and percentage
Clinical and research settings usually report LBM in kilograms; US gym and nutrition contexts often use pounds. This tool converts automatically. Percentage here means LBM as a share of total weight (and estimated fat % as the remainder from Boer), not body fat measured on a scan.
Fat-free mass vs lean body mass vs muscle mass
What is LBM? — non-fat body mass. Fat-free mass (FFM) is often used as a synonym in fitness apps, though purists reserve a few hundred grams for essential fat in FFM definitions. Lean body mass vs fat-free mass is usually a small semantic difference, not a separate measurement on this page. Neither LBM nor FFM equals muscle mass alone — bone, organs and fluid contribute substantially.
Anesthesia, protein, BMR, TDEE & macros
Anesthesia and critical-care lectures sometimes reference lean or ideal body size for ventilator and drug-volume teaching — follow your institution’s protocol, not an online estimate alone. Protein intake guides (for example grams per kg LBM per day in sports nutrition) use estimated LBM when DEXA is unavailable. Some BMR equations (Katch–McArdle and similar) use LBM instead of total weight; TDEE and macro planning often start from BMR × activity factor. This page explains those links for education — it is not a full TDEE or macro calculator and does not prescribe diets or drug doses.
For kidney-related dosing context, pair LBM estimates with the creatinine clearance calculator, ideal body weight calculator, and BMI calculator when protocols reference habitus or lean size.
Calculation example
Female, height 165 cm, weight 50 kg — the Example button loads this case.
- Boer LBM = 0.252 × 50 + 0.473 × 165 − 48.3 = 12.6 + 78.0 − 48.3 ≈ 42.3 kg (≈ 93.3 lb).
- LBM % ≈ 42.3 ÷ 50 ≈ 84.6%; estimated fat mass ≈ 7.7 kg (~15.4% fat).
- James and Hume on the same inputs land near 40–41 kg — compare in the results table.
If measured body fat were 22%, BF-method LBM = 50 × 0.78 = 39.0 kg, which you can enter in the optional field.
Lean body mass FAQ
What is lean body mass (LBM)?
Non-fat body mass including muscle, bone, organs and water — estimated here from anthropometrics or from body fat % when provided.
What is the Boer formula for lean body mass?
Men: 0.407×weight(kg) + 0.267×height(cm) − 19.2. Women: 0.252×weight + 0.473×height − 48.3. Results are in kilograms.
Boer vs James vs Hume — which should I use?
Boer is the default primary result on this page. James and Hume are shown for comparison. Use measured body fat % when you have it.
How do I calculate LBM with body fat percentage?
LBM = weight × (1 − BF%/100). Enter BF% in the optional field to compare with Boer.
Is there an LBM calculator for men and women?
Yes — select Female or Male. All three formulas change coefficients by sex.
Lean body mass vs fat-free mass — same thing?
Often used interchangeably in fitness. Strict FFM definitions may exclude essential fat; calculator output treats them as the same estimate.
Is lean body mass the same as muscle mass?
No. Muscle is only part of LBM. Bone, organs, blood and water are included too.
Can I get lean body mass in kg and pounds?
Yes. Primary Boer LBM shows kg and lb after you calculate, with kg/lb input swaps.
How is LBM used for protein, BMR and TDEE?
Many guides scale protein to LBM; some BMR formulas use LBM. This page does not compute full TDEE or macro plans.
Is LBM used in anesthesia or medical dosing?
Sometimes referenced in teaching for lean-size estimates. Always follow labels and local protocols.
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User Reviews
4.9 / 5 from 3 recent users of this lean body mass calculator
Boer LBM with James and Hume side-by-side is perfect for teaching macro protein ranges. Body fat % override is clearly labeled.
Fast kg/lb swap and composition breakdown help connect LBM to dosing lectures without pretending to be a full TDEE calculator.
Good explanation of LBM vs muscle mass. Example case matches what I use with clients at 165 cm.
Related size and kidney tools: ideal body weight calculator, BMI calculator, body surface area calculator, and creatinine clearance calculator.