Lean Body Mass Calculator
Estimate your lean body mass from three published formulas.
Lean Body Mass Calculator — your inputs
- Sex
- Male
- Height
- 180 cm
- Weight
- 80 kg
- Unit system
- Metric
Key takeaways
- Lean body mass is everything that is not fat: muscle, bone, organs and water. Usually 60–90% of body weight.
- Like the ideal-weight formulas, these were derived for clinical purposes — Boer's for normalising body fluid volumes, not for tracking gym progress.1
- They estimate from height and weight alone, so they cannot detect whether you have gained muscle at a stable weight. That is their central limitation.
- Preserving lean mass in a deficit is the goal: protein plus resistance training is what does it, and the effect is large.5
- For a direct estimate that responds to your actual body, use the Body Fat Calculator — lean mass is simply weight minus fat mass.
How to use this calculator
Choose your unit system, sex, height, and weight.
The calculator shows all three formula estimates, their average, and the implied fat mass.
Understanding your result
Lean body mass is everything that isn't fat — muscle, bone, organs, and water. It's useful for dosing some medications and for estimating metabolic needs.
The three formulas here use height and weight regressions; they agree closely for most adults but diverge at the extremes.
What lean body mass includes
Lean body mass is a subtraction: total weight minus fat mass. What remains is skeletal muscle, bone, organs, connective tissue and the water in all of it. Skeletal muscle is usually the largest single component, but it is not the whole thing — which matters, because people often read a lean mass figure as a muscle figure and it is not.
| Component | Share of lean mass |
|---|---|
| Skeletal muscle | ~50% |
| Body water outside muscle | ~20% |
| Bone | ~15% |
| Organs, blood, connective tissue | ~15% |
Why the number moves when nothing has changed
A high-carbohydrate day, a hard training session, or a salty meal can each shift body water by a kilogram or more. Lean mass estimates track that water. Read the trend across weeks, never two consecutive days.
The three formulas and what they can't do
Boer (1984), James (1976) and Hume (1966) all take the same two inputs — height and weight — plus sex, and return an estimate.123 They were fitted to different populations for different clinical purposes: Boer's to normalise fluid volumes in renal medicine, Hume's for pathology work, James's as part of a UK obesity research report.
The consequence is worth stating plainly, because it is the single most common misunderstanding about this calculator. If your weight and height do not change, these formulas cannot change either. Someone who spends a year replacing five kilograms of fat with five kilograms of muscle — a genuinely excellent outcome — will get an identical answer on both days. The formulas do not know anything about your body composition; they know the average composition of a person your size.
Use this alongside a direct measure, not instead of one
The Body Fat Calculator uses tape measurements that respond to your actual shape. Weight minus fat mass from that is a lean-mass estimate that will actually move when your body does.
Why lean mass is worth protecting
Two reasons, one metabolic and one that becomes more important every decade.
- It sets your metabolic floor. Lean tissue is what your BMR mostly reflects. Lose muscle during a diet and you lower the calorie level at which you can maintain your new weight — which is exactly the wrong direction.
- It determines what you can do later. The European consensus on sarcopenia defines the condition primarily by muscle strength and mass, and links it to falls, fractures, loss of independence and mortality.4 Muscle built in your thirties and forties is the reserve you draw on in your seventies.
The good news is that the intervention is well established and the effect is not marginal. Longland and colleagues put participants in a steep deficit for four weeks with resistance training, and compared higher protein (2.4 g/kg) against lower (1.2 g/kg). The high-protein group gained 1.2 kg of lean mass while losing fat; the lower-protein group merely held theirs.5 Same deficit, same training, very different body composition outcome.
- 2.4 g/kg protein1.2 kg change
Gained lean mass while dieting
- 1.2 g/kg protein0.1 kg change
Essentially maintained
| Method | Value (kg change) |
|---|---|
| 2.4 g/kg protein | 1.2 |
| 1.2 g/kg protein | 0.1 |
What to do about it
- Set protein deliberately. The Protein Calculator gives a target by bodyweight and goal. In a deficit, aim high in the range.
- Lift. Resistance training two to four times a week is the signal that tells the body to keep the muscle. Without it, protein alone does much less.
- Keep the deficit moderate. Steeper deficits lose proportionally more lean mass. The Calorie Calculator defaults to a sustainable rate for this reason.
- Track something that can actually change. Tape measurements, strength in the gym, or how clothes fit. All three respond to body recomposition; a height-and-weight formula does not.
Terms used on this page
- Lean body mass
- Total body weight minus fat mass. Includes muscle, bone, organs and water — not muscle alone, which is a common misreading.
- Fat-free mass
- Used almost interchangeably with lean body mass. Strictly, fat-free mass excludes the essential fat within cell membranes and organs, so it is very slightly smaller.
- Sarcopenia
- Age-related loss of muscle mass and strength. Defined by the European consensus primarily through strength, and associated with falls, fractures and loss of independence.
- Body recomposition
- Losing fat and gaining muscle at the same time, so weight barely moves. Most achievable in beginners, people returning after a break, and those starting with higher body fat.
The formula
- Man, height 180 cm, weight 80 kg
- Boer: 0.407×80 + 0.267×180 − 19.2 = 32.56 + 48.06 − 19.2
Source: Boer, James, Hume. Published clinical/scientific formula.
Limitations
- These are regression estimates, not a substitute for direct body-composition testing (DEXA, hydrostatic).
- They are less accurate at extreme heights and weights.
References
- 1.Estimated lean body mass as an index for normalization of body fluid volumes in humans. Boer, P., American Journal of Physiology 247(4):F632–F636, 1984.
- 2.Research on Obesity: A Report of the DHSS/MRC Group. James, W.P.T., Her Majesty's Stationery Office, London, 1976.
- 3.Prediction of lean body mass from height and weight. Hume, R., Journal of Clinical Pathology 19(4):389–391, 1966.
- 4.Sarcopenia: revised European consensus on definition and diagnosis (EWGSOP2). Cruz-Jentoft et al., Age and Ageing 48(1):16–31, 2019.
- 5.Effects of dietary protein and resistance training on lean mass retention during energy restriction. Longland et al., American Journal of Clinical Nutrition 103(3):738–746, 2016.
Frequently asked questions
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Read articleNot medical advice. This calculator is for general informational purposes only and is not a substitute for professional medical guidance. Always consult a qualified healthcare provider before making decisions about your health. Read the full medical disclaimer.
Printed from mystatura.com — for general information only, not medical advice.