💪 Lean Body Mass Calculator
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, health content · Updated 2026-06-19
This calculator gives an estimate for healthy adults and is not medical advice. Lean body mass varies with muscle, bone density, hydration and body type, and formulas are less reliable at the extremes of weight. Speak to a doctor or registered dietitian before making decisions based on these numbers.
Estimated with the Boer formula. Lean body mass is everything in your body except stored fat.
Lean body mass (LBM) is everything in your body that is not stored fat: muscle, bone, organs, connective tissue and the water inside them. This calculator uses the Boer formula, a widely cited equation that estimates LBM from your sex, weight and height. Enter your details in metric or imperial units to see your lean body mass, your body fat mass (total weight minus LBM), and what share of your weight is lean tissue.
What is the Lean Body Mass Calculator?
Your body weight is made up of two broad parts: fat mass and lean body mass. Fat mass is the energy your body stores as adipose tissue. Lean body mass, sometimes called fat free mass, is everything else, and it is the part that burns most of your resting calories and does the physical work of moving you around. Tracking LBM rather than raw weight tells you whether a diet or training plan is protecting muscle or stripping it away.
The Boer formula, published by P. Boer in 1984, estimates LBM from weight in kilograms and height in centimetres, with a different equation for each sex. For men it is 0.407 multiplied by weight in kg, plus 0.267 multiplied by height in cm, minus 19.2. For women it is 0.252 multiplied by weight in kg, plus 0.473 multiplied by height in cm, minus 48.3. The two equations differ because, at the same height and weight, men typically carry more lean tissue and less fat than women.
Because the Boer formula uses only weight and height, it cannot measure your actual body composition the way a DEXA scan, hydrostatic weighing or a skinfold test can. It assumes a fairly typical build, so a very muscular athlete or a person carrying a lot of excess fat may see a less accurate result. Treat the output as a reasonable estimate and a baseline you can track over time, not a precise clinical measurement.
When to use it
- Estimating how much of your weight is muscle and lean tissue versus stored fat.
- Tracking whether a cutting diet is preserving lean body mass or causing muscle loss.
- Working out a protein target or a medication dose that is based on lean mass rather than total weight.
- Setting a realistic body composition goal alongside a simple bathroom scale reading.
How to use the Lean Body Mass Calculator
- Choose metric (kg and cm) or imperial (lb and ft-in) units.
- Select your sex, since the Boer formula uses a different equation for men and women.
- Enter your current weight and height.
- Read your lean body mass, your body fat mass, and the percentage of your weight that is lean tissue.
Formula & method
Worked examples
A man weighing 80 kg at 180 cm tall.
- LBM = 0.407 × 80 + 0.267 × 180 − 19.2
- = 32.56 + 48.06 − 19.2
- = 61.42 kg
- Body fat mass = 80 − 61.42 = 18.58 kg
Result: LBM about 61.4 kg, body fat mass about 18.6 kg (lean mass is roughly 77% of weight)
A woman weighing 65 kg at 165 cm tall.
- LBM = 0.252 × 65 + 0.473 × 165 − 48.3
- = 16.38 + 78.045 − 48.3
- = 46.13 kg (rounded)
- Body fat mass = 65 − 46.13 = 18.88 kg
Result: LBM about 46.1 kg, body fat mass about 18.9 kg (lean mass is roughly 71% of weight)
Common lean body mass formulas and what they use
| Formula | Year | Inputs used | Notes |
|---|---|---|---|
| Boer | 1984 | Sex, weight, height | Used on this page; popular for general estimates and dosing. |
| James | 1976 | Sex, weight, height | Older equation; can underestimate LBM at higher weights. |
| Hume | 1966 | Sex, weight, height | Derived from body water measurements. |
Typical body fat percentage ranges for adults (ACE guidelines)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletes | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Above average | 25% and over | 32% and over |
Common mistakes to avoid
- Treating the estimate as a measurement. The Boer formula uses only weight and height, so it cannot see your real muscle or fat. For an accurate figure you need a DEXA scan, hydrostatic weighing or skinfold testing.
- Mixing units. Entering height in centimetres but weight in pounds (or the reverse) gives a meaningless result. Pick metric or imperial and keep both inputs in the same system.
- Confusing lean body mass with muscle mass. Lean body mass includes bone, organs and body water, not just skeletal muscle. Your muscle alone is only part of your LBM, so do not read the LBM figure as your muscle weight.
- Expecting accuracy at the extremes. The formula assumes a fairly typical build. Very muscular athletes and people carrying a lot of excess fat will see results that drift from their true composition.
Glossary
- Lean body mass (LBM)
- The weight of everything in your body except stored fat: muscle, bone, organs, connective tissue and body water.
- Fat free mass
- Another name for lean body mass, used to stress that it excludes all stored body fat.
- Body fat mass
- The weight of fat stored in your body, equal to your total weight minus your lean body mass.
- Boer formula
- A 1984 equation that estimates lean body mass from sex, weight and height.
- Body composition
- The proportions of fat, muscle, bone and water that make up your total body weight.
Frequently asked questions
What is lean body mass?
Lean body mass (LBM) is the total weight of everything in your body that is not stored fat. That includes muscle, bone, organs, skin, connective tissue and the water held inside them. It is sometimes called fat free mass.
How is the Boer formula calculated?
For men, LBM equals 0.407 multiplied by weight in kg, plus 0.267 multiplied by height in cm, minus 19.2. For women, it is 0.252 multiplied by weight in kg, plus 0.473 multiplied by height in cm, minus 48.3. Body fat mass is your total weight minus your LBM.
What is the difference between lean body mass and muscle mass?
Muscle mass is only the weight of your skeletal muscle. Lean body mass is broader: it also includes bone, organs, connective tissue and body water. Your muscle is a large part of LBM but not all of it, so the two figures are not the same.
Why does the formula use different equations for men and women?
At the same height and weight, men on average carry more lean tissue and less body fat than women. The Boer formula captures this difference with separate constants and multipliers for each sex, which gives a more realistic estimate.
How accurate is this lean body mass calculator?
It is a reasonable estimate for adults of typical build but not a measurement. Because it uses only weight and height, it cannot see your actual fat or muscle. For precise body composition use a DEXA scan, hydrostatic weighing or skinfold testing.
Does this calculator store my data?
No. The calculation runs entirely in your browser using JavaScript. Nothing you enter is sent to a server or saved anywhere.
Sources
- Estimated lean body mass as an index for normalization of body fluid volumes (Boer) , American Journal of Physiology (1984)
- Percent Body Fat Norms and Body Composition , American Council on Exercise (ACE)