On This Page
- What lean body mass means
- Formulas, Boer, James, and Hume
- Women and men
- How to calculate manually
- From body fat percentage
- Ideal and maximum LBM
- Protein, BMR, and TDEE
- Worked examples
- Frequently asked questions
How to Use This Calculator
Enter sex, weight, and height. The result shows lean body mass, estimated fat mass, lean mass percentage, and estimates from all three equations, Boer, James, and Hume, side by side. The spread between them gives a realistic sense of the uncertainty built into any height-and-weight formula. If you already know your body fat percentage from a DEXA scan or skinfold test, the body fat percentage method below gives a more accurate result than any formula. To cross-reference with a WHO weight classification at the same height and weight, the BMI Calculator returns the standard category and healthy weight range from the same two measurements. If you are of South Asian, East Asian, or Southeast Asian descent, the Asian BMI Calculator applies the WHO-adjusted thresholds that better reflect metabolic risk in those populations.
What Is Lean Body Mass?
Lean body mass (LBM) is the combined weight of everything in your body except fat: muscle, bone, organs, water, and connective tissue. It is not the same as muscle mass, muscle is typically the largest component of LBM, but bone density, organ size, and hydration each contribute meaningfully to the total. Because body water is a component of LBM, daily hydration affects readings — the Water Intake Calculator gives a weight-adjusted daily fluid target to keep hydration stable as a variable.
In strict research terminology, fat-free mass excludes all lipids including essential fat, while lean body mass includes a small amount of essential fat (~3% for men, ~12% for women). In practice, the two terms are used interchangeably in most fitness and nutrition contexts and the difference has no effect on planning decisions.
Formulas, Boer, James, and Hume
No single height-and-weight formula is perfect. All three are population-derived regression equations, they perform well on average but can be off by several kilograms for individuals at extreme heights, weights, or muscle levels. The calculator uses Boer as the primary estimate because it shows the best average accuracy for typical adults; James and Hume are shown for comparison.
Boer
- Male: LBM = 0.407W + 0.267H − 19.2
- Female: LBM = 0.252W + 0.473H − 48.3
James
- Male: LBM = 1.1W − 128(W/H)²
- Female: LBM = 1.07W − 148(W/H)²
Hume
- Male: LBM = 0.32810W + 0.33929H − 29.5336
- Female: LBM = 0.29569W + 0.41813H − 43.2933
In all equations, W is weight in kilograms and H is height in centimetres. James tends to run slightly higher than Boer; Hume tends to run slightly lower. When all three are close together, the estimate is more reliable. A wide spread between them, which can happen at very high or very low body weights, signals higher uncertainty.
Women and Men
LBM differs between sexes because of hormonal differences that affect muscle mass, bone density, and the amount of essential fat each body must maintain.
Men
Men carry a higher lean mass fraction. At average body fat levels, lean mass typically represents 70–80% of total body weight; at lower body fat, 80–90%. Competitive male athletes often sit at 85–92% lean.
Boer male example: 75 kg, 175 cm → LBM = 0.407(75) + 0.267(175) − 19.2 = 30.5 + 46.7 − 19.2 = 58.0 kg (77% lean).
Women
Women maintain more essential fat for hormonal function, so lean mass percentage is lower at the same apparent fitness level. A typical healthy range is 70–85% of total body weight.
Boer female example: 60 kg, 165 cm → LBM = 0.252(60) + 0.473(165) − 48.3 = 15.1 + 78.0 − 48.3 = 44.8 kg (75% lean).
How to Calculate Manually
All three formulas require weight in kilograms and height in centimetres. Convert US measurements first if needed.
Then substitute into whichever formula you're using. To convert the result back to pounds: lb = kg × 2.2046.
From Body Fat Percentage
When you have a measured body fat percentage, from DEXA, hydrostatic weighing, Bod Pod, or skinfold calipers, this method is more accurate than any height-and-weight formula.
Express body fat as a decimal: 20% = 0.20. Example: 180 lb at 20% body fat → LBM = 180 × 0.80 = 144 lb.
Ideal and Maximum LBM
There is no universal ideal LBM target. A practical approach is to work backwards from a goal weight and target body fat percentage:
Example: goal of 170 lb at 15% body fat → ideal LBM = 170 × 0.85 = 144.5 lb. This tells you how much of that goal weight should be lean tissue.
Maximum natural LBM
A rough estimate of maximum lean body mass at competition-level leanness (~5% body fat for men), popularised by Martin Berkhan:
At 180 cm, that gives a rough natural ceiling of ~80 kg LBM at peak leanness. Individual variation is large, bone structure and genetics move this number considerably. Treat it as a rough planning reference, not a hard limit.
LBM percentage and lean body mass index
Lean mass percentage = LBM ÷ body weight × 100. The lean body mass index applies the BMI structure to lean tissue: LBMI = LBM (kg) ÷ height (m)². Both are shown automatically in the result panel.
Protein, BMR, and TDEE
Fat mass is metabolically far less active than muscle and organs. Using LBM rather than total body weight to set protein and calorie targets produces more accurate numbers for people carrying significant body fat.
Protein
- Maintenance / moderate activity: 0.7–0.8 g per lb of LBM
- Muscle building: 0.8–1.0 g per lb of LBM
- Fat loss: 1.0–1.2 g per lb of LBM (higher intake helps preserve lean tissue in a deficit)
Example: 150 lb LBM at 0.8 g/lb = 120 g protein per day.
BMR, Katch-McArdle formula
Katch-McArdle estimates basal metabolic rate directly from lean body mass, which means it doesn't need separate sex and age inputs, lean mass already reflects those differences.
At 58 kg LBM: BMR = 370 + (21.6 × 58) = 1,622.8 kcal/day. This formula tends to be more reliable for lean and athletic individuals than Harris-Benedict or Mifflin-St Jeor.
TDEE
- Sedentary (little/no exercise): × 1.2
- Light activity (1–3 days/week): × 1.375
- Moderate activity (3–5 days/week): × 1.55
- Very active (6–7 days/week): × 1.725
- Twice-daily training: × 1.9
Macros
Once protein is set from LBM, the remaining calories split between fat and carbohydrates based on preference and training demands. A common starting point for body recomposition:
- Protein: 1 g/lb LBM × 4 kcal/g
- Fat: 0.35–0.45 g/lb total weight × 9 kcal/g
- Carbohydrates: remaining calories
Worked Examples
Example 1, LBM in kg (Boer, male)
Male, 75 kg, 175 cm.
- LBM = 0.407(75) + 0.267(175) − 19.2
- = 30.525 + 46.725 − 19.2 = 58.1 kg
Example 2, LBM in pounds (Boer, female)
Female, 145 lb, 65 in.
- Convert: 145 × 0.4536 = 65.77 kg; 65 × 2.54 = 165.1 cm
- LBM = 0.252(65.77) + 0.473(165.1) − 48.3 = 16.57 + 78.09 − 48.3 = 46.36 kg
- Convert back: 46.36 × 2.2046 = 102.2 lb
Example 3, From body fat percentage
Person, 187 lb, 17% body fat.
- LBM = 187 × (1 − 0.17) = 187 × 0.83 = 155.2 lb
Example 4, Lean mass percentage
Person, 80 kg total, 62 kg LBM.
- 62 ÷ 80 × 100 = 77.5%
Example 5, Protein target from LBM
LBM 150 lb, target 0.8 g/lb.
- 150 × 0.8 = 120 g protein/day
Frequently Asked Questions
How do you calculate lean body mass?
Two approaches. With height and weight: use the Boer, James, or Hume equation (weight in kg, height in cm). With a measured body fat percentage: LBM = body weight × (1 − body fat%). The body fat percentage method is more accurate when you have a real measurement from DEXA, skinfold, or another test.
How do you calculate LBM from body fat percentage?
Convert body fat percentage to a decimal and multiply body weight by what remains. Example: 180 lb at 20% body fat → LBM = 180 × (1 − 0.20) = 144 lb.
How do you calculate LBM in kg or pounds?
Select Metric to get the result in kg; select US to get it in pounds. For manual calculation, apply the formulas with weight in kg and height in cm, then multiply by 2.2046 to convert the result to pounds.
How do you calculate lean mass percentage?
LBM ÷ body weight × 100. The calculator shows this in the result panel. Example: 62 kg LBM at 80 kg body weight = 62 ÷ 80 × 100 = 77.5%.
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.
Which formula is most accurate, Boer, James, or Hume?
Boer has the best average accuracy for typical adults and is the default here. James runs slightly higher; Hume slightly lower. All three are population-derived estimates, they can be off by several kilograms for people with very high or very low muscle mass, or at extreme heights and weights. A DEXA scan or hydrostatic weighing result will always be more reliable than any formula.
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.