On This Page
- Everything that isn't fat
- Measured or estimated?
- Three formulas, one headline number
- Men, women and lean percentage
- Putting LBM to work: protein and calories
- Setting a target
- How the calculator is verified
- FAQ
Everything That Isn't Fat
Lean body mass (LBM) is muscle, bone, organs, water and connective tissue, so it is not the same as muscle mass. Because water is part of it, hydration moves the number. The Water Intake Calculator helps keep that steady, and how much water to drink in hot weather covers heat. Strict research language separates "fat-free mass" (no fat at all) from LBM (a little essential fat), but fitness planning treats them as the same.
Measured or Estimated?
If you have a body fat percentage from DEXA, a Bod Pod, hydrostatic weighing or calipers, use it, because it beats any formula:
180 lb at 20% is 144 lb lean, and 187 lb at 17% is 155.2 lb. Without a measurement, enter sex, weight and height and the calculator estimates LBM, fat mass and lean percentage from three published equations. For a weight category from the same two measurements, use the BMI Calculator; the Asian BMI Calculator applies the lower cutoffs for people of Asian descent.
Three Formulas, One Headline Number
W is weight in kg and H is height in cm. For a man of 75 kg and 175 cm:
| Formula | Men | Women | 75 kg, 175 cm man |
|---|---|---|---|
| Boer (headline) | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 | 58.1 kg |
| James | 1.1W − 128(W/H)² | 1.07W − 148(W/H)² | 59.0 kg |
| Hume | 0.32810W + 0.33929H − 29.5336 | 0.29569W + 0.41813H − 43.2933 | 54.4 kg |
All three are population averages and can miss by several kilograms for very muscular, very tall or very heavy people. When they agree, trust the estimate more; a wide spread means more uncertainty. To work in pounds by hand, use kg = lb × 0.4536 and cm = in × 2.54, then lb = kg × 2.2046. A woman of 145 lb and 65 in comes out at 46.37 kg, or 102.2 lb. To run the formula down a whole list, the fill-down method in calculating BMI in Excel works the same way.
Men, Women and Lean Percentage
Lean percentage = LBM ÷ weight × 100, and the calculator shows it next to the result: 62 kg lean at 80 kg is 77.5%. Men usually sit at 70–80% lean, 80–90% when lean, and 85–92% as athletes. Women carry more essential fat, so a healthy range is about 70–85%. A woman of 60 kg and 165 cm comes out at 44.9 kg lean (about 75%) by Boer. LBM is one view of body composition; waist size and waist-to-height ratio flags belly-fat risk that lean mass cannot.
Putting LBM to Work: Protein and Calories
Fat burns little energy and needs little protein, so targets based on lean mass fit people with more body fat better than targets based on total weight.
- Protein: 0.7–0.8 g per lb of LBM to maintain, 0.8–1.0 to build muscle, 1.0–1.2 while cutting. 150 lb lean × 0.8 = 120 g a day.
- BMR (Katch-McArdle): 370 + 21.6 × LBM in kg. 58 kg lean gives about 1,623 kcal a day. It needs no age or sex input because lean mass already reflects them.
- TDEE: BMR × 1.2 (sedentary), 1.375 (1–3 days of exercise a week), 1.55 (3–5), 1.725 (6–7) or 1.9 (twice a day).
- Macros: set protein from LBM, fat at about 0.35–0.45 g per lb of total weight, and fill the rest with carbohydrates.
Setting a Target
A goal weight and body fat give a lean target: 170 lb at 15% means 144.5 lb lean. For a rough natural ceiling at contest leanness, Martin Berkhan's rule of thumb is height in cm − 100 kg, so about 80 kg at 180 cm. Genetics and frame move that a lot. Lean body mass index, LBM in kg ÷ height in m², is a by-hand way to compare lean mass across heights.
How the Calculator Is Verified
Enter the same height, weight, and sex once, and the page runs all three regression equations, Boer, James, and Hume, against that identical input set. Each has its own male and female coefficients: Boer subtracts 19.2 from a weighted sum for men and 48.3 for women, James uses a squared weight-to-height ratio term instead of a linear one, and Hume applies a third, separate set of constants again. Only the Boer result feeds the fat mass and lean mass percentage shown above the comparison table; the James and Hume figures sit alongside it for reference but are not blended into that headline number.
Frequently Asked Questions
Should protein intake be based on LBM or total weight?
LBM gives a better target when body fat is elevated, because fat tissue drives very little protein requirement. At higher body fat levels, using total body weight overshoots by a meaningful margin. A range of 0.7–1.0 g per lb of LBM covers most active individuals; go toward the high end when in a calorie deficit.
Is lean body mass the same as muscle mass?
No. LBM is everything that isn't fat, muscle, bone, organs, body water, and connective tissue. Muscle is usually the largest single component, but bone density and hydration affect the number too. You can gain or lose LBM without changing muscle mass, and vice versa.
How does WHOOP estimate lean body mass?
WHOOP uses a height-and-weight formula (similar to Boer or James) combined with the sex in your profile. It does not directly measure body composition. If your WHOOP reading differs from this calculator, it's using a different equation or rounding convention, both are approximations, not measurements.
References
- Body Composition Methods, NIH / PubMed Central: peer-reviewed overview of lean body mass measurement techniques and accuracy compared to reference methods.
- Boer P. (1984), Estimated lean body mass as an index, PubMed: original Boer equation derivation for lean body mass estimation.
- CDC NHANES body composition data: population reference data underlying lean mass norms and formula validation.