Calculate lean body mass (LBM) — your total body weight minus fat mass — using multiple validated formulas. Used for medication dosing and fitness planning.
Lean body mass (LBM) is your total body weight minus your fat mass. It includes your muscles, bones, organs, blood and water — everything that is not body fat. For most adults, lean body mass makes up around 60–90% of total weight, and it is higher in men and in physically active people. It is also called fat-free mass.
| Formula | LBM (kg) |
|---|
There are two common ways to calculate lean body mass: from your body fat percentage, or from height and weight using a validated formula like Boer, James or Hume.
Each formula was developed from a different population, so results vary slightly. Boer is the most widely recommended today.
| Formula | Best For | Notes |
|---|---|---|
| Boer (1984) | General use — the modern default | Accurate for most adults |
| James (1976) | Clinical and older reference use | Can under-estimate in heavier people |
| Hume (1966) | Historical, still cited | Oldest of the three |
People often assume lean body mass is the same as muscle, but muscle is only one part of it. This is a key distinction competitors usually skip.
| Feature | Lean Body Mass | Muscle Mass |
|---|---|---|
| What it includes | Muscle + bone + organs + water + blood | Only skeletal muscle |
| Share of body | ~60–90% of weight | ~30–40% of weight |
| Easy to measure? | Yes — from weight and body fat | Harder — needs a scan |
| Changes with training | Rises modestly | Rises with strength training |
Lean body mass and fat-free mass are often used to mean the same thing, and for everyday purposes they are close. The technical difference is small: fat-free mass excludes all fat, while lean body mass includes the small amount of essential fat stored inside organs and the nervous system. In practice, most calculators — including this one — treat them as equivalent.
You can build lean body mass gradually and safely. The evidence points consistently to a few habits:
LBM is the weight of everything in your body except fat: muscles, bones, organs, skin, and water. It is used in medicine for drug dosing, in sports for performance tracking, and in fitness for setting protein intake targets.
The NHMRC recommends 0.75–1.0 g protein per kg body weight for sedentary adults. Athletes and resistance trainers may need 1.2–2.0 g/kg LBM per day.
Lean Body Mass (LBM) is the portion of your total body weight that is not fat — including muscle, bone, organs, water, and connective tissue. It is sometimes confused with muscle mass, but LBM encompasses all non-fat tissues. For fitness tracking, LBM is more useful than body weight alone because it tells you whether changes are from fat loss, muscle gain, or fluid shifts.
| Formula | Men | Women |
|---|---|---|
| Boer (most validated) | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 |
| James | 1.1W − 128(W/H)² | 1.07W − 148(W/H)² |
| Hume | 0.3281W + 0.3393H − 29.5336 | 0.29569W + 0.41813H − 43.2933 |
W = weight in kg | H = height in cm. Different formulas give slightly different results — the calculator shows all three and the average for comparison.
What is lean body mass and how is it different from muscle mass?
Lean body mass (LBM) includes everything in your body except fat — muscle, bone, organs, water, blood, and connective tissue. Muscle mass is a subset of LBM. The distinction matters: you can increase LBM through bone density improvements or water retention, not just muscle building. For fitness tracking, skeletal muscle mass (measured by DEXA) is the most useful specific metric.
What is a good lean body mass?
There is no universal 'good' LBM number — it depends on height, sex, and fitness goals. LBM as a percentage of body weight is more useful: for men, 75-85% LBM is typical for a healthy weight adult; for women, 65-75% is typical. Elite athletes may have higher LBM% through greater muscle mass combined with low body fat.
How do I increase my lean body mass?
Resistance training (weight training) is the most effective way to increase LBM by building skeletal muscle. Adequate protein intake (1.6-2.2g/kg/day) provides the building blocks for muscle protein synthesis. Progressive overload — gradually increasing training volume and intensity — is the key principle. Calorie surplus (100-300 calories above TDEE) supports muscle growth without excessive fat gain.
How do I calculate my lean body mass?
You can calculate it two ways. If you know your body fat percentage, this body fat lean mass method simply subtracts your fat weight from your total weight. Otherwise use a formula like Boer, which needs only your height, weight and sex. The calculator above applies all methods and shows the results side by side.
How is lean body mass calculated from body fat percentage?
Multiply your body weight by your body fat percentage to get your fat mass, then subtract that from your total weight. For example, an 80 kg person at 20% body fat has 16 kg of fat, giving a lean body mass of 64 kg. This is the most direct method when body fat is known.
What is the difference between lean body mass and muscle mass?
Lean body mass includes everything that is not fat — muscle, bone, organs, water and blood. Muscle mass is only the skeletal muscle portion. So your lean body mass is always larger than your muscle mass; muscle typically makes up around a third of body weight, while lean mass can be 60–90%.
Is lean body mass the same as fat-free mass?
For everyday use, yes — the two terms are usually treated as the same. Technically, fat-free mass excludes all fat, while lean body mass includes the tiny amount of essential fat inside organs and the nervous system. The difference is small and most calculators use them interchangeably.
What is a healthy lean body mass percentage?
It varies by sex and fitness. Men typically have a lean mass of around 80–90% of body weight, and women around 70–85%, with the rest being body fat. Athletes sit at the higher end. Rather than a single target, aim to maintain or gradually build lean mass over time.
Why does lean body mass matter for metabolism?
Lean tissue is metabolically active, so it burns more calories at rest than fat does. That means people with more lean body mass tend to have a higher BMR (resting calorie burn). Preserving lean mass while losing fat is a key goal of healthy weight loss.
How often should I recalculate my lean body mass?
Every one to three months is enough for most people, or whenever your weight or body fat changes noticeably. Because building lean mass is slow, checking too often can be discouraging — track the longer-term trend instead of small week-to-week changes.