Which formula is most accurate?

The Boer (1984) formula is widely considered the most accurate for most adults and is the default selection. The James formula can produce negative LBM for very obese individuals, which is a known limitation. Hume provides a useful alternative check. For the most accurate body composition measurement, methods like DXA scanning or hydrostatic weighing are far superior to any formula.

How does LBM differ from muscle mass?

LBM includes muscle mass but also bone, organs, connective tissue, blood, and water. Muscle mass alone is typically estimated to be around 30–55% of body weight in healthy adults, depending on fitness level. LBM is a broader category.

What is a healthy body fat percentage?

According to the American Council on Exercise (ACE), essential fat is 2–5% for males and 10–13% for females. Athletic ranges are 6–13% (male) and 14–20% (female). Fitness ranges are 14–17% (male) and 21–24% (female). Obese is generally >25% (male) and >32% (female).

Can I use LBM to calculate my protein needs?

Yes. Many nutritionists recommend setting protein intake based on LBM rather than total body weight. A common recommendation is 1.6–2.2 g of protein per kg of LBM per day for individuals engaged in resistance training.

Lean Body Mass Calculator

Your lean body mass (LBM) — also called fat-free mass (FFM) — is everything your body is made of except fat. It includes muscle tissue, bones, organs, blood, and water. Knowing your LBM is one of the most useful metrics for athletes, fitness enthusiasts, and anyone interested in understanding their body composition beyond a simple scale number or BMI.

What Is Lean Body Mass?

Lean body mass is the component of your total body weight that is not fat. Mathematically:

LBM = Total Body Weight − Fat Mass

A person weighing 80 kg with 20% body fat has a fat mass of 16 kg and an LBM of 64 kg.

LBM is important because it is the metabolically active component of your body. Muscle, liver, kidneys, and heart tissue burn many more calories at rest than fat tissue. This is why two people of identical weight can have very different calorie needs based on their body composition.

The Three Formulas

This calculator supports three validated anthropometric LBM estimation formulas:

Boer (1984) — Recommended for general use. Derived from a clinical study of intensive care patients (Boer P., Critical Care Medicine, 1984):

Male: LBM = 0.407 × W + 0.267 × H − 19.2
Female: LBM = 0.252 × W + 0.473 × H − 48.3

Where W = weight in kg, H = height in cm.

James (1976) — From the original HMSO research on obesity (James WPT, 1976):

Male: LBM = 1.1 × W − 128 × (W/H)²
Female: LBM = 1.07 × W − 148 × (W/H)²

Note: The James formula can produce negative or unrealistic values for individuals with a very high weight-to-height ratio (i.e., very obese). Use with caution.

Hume (1966) — One of the earliest validated formulas (Hume R., J Clin Pathol, 1966):

Male: LBM = 0.3281 × W + 0.33929 × H − 29.5336
Female: LBM = 0.29569 × W + 0.41813 × H − 43.2933

How to Use This Calculator

Select your biological sex — this determines which formula constants apply.
Enter your weight in kilograms. Accurate results require accurate input; weigh yourself in the morning before eating.
Enter your height in centimetres.
Choose your formula — Boer is recommended for most users. If you want to compare results, try all three.
Review your results — the calculator shows your estimated LBM in kg and lb, estimated body fat mass, and body fat percentage.

Examples

Example 1: Male, 75 kg, 178 cm (Boer)

LBM = 0.407 × 75 + 0.267 × 178 − 19.2 = 30.525 + 47.526 − 19.2 = 58.85 kg (129.7 lb)

Body fat mass = 75 − 58.85 = 16.15 kg Body fat % = 16.15 / 75 × 100 = 21.5%

Example 2: Female, 62 kg, 165 cm (Boer)

LBM = 0.252 × 62 + 0.473 × 165 − 48.3 = 15.624 + 78.045 − 48.3 = 45.37 kg (100.0 lb)

Body fat mass = 62 − 45.37 = 16.63 kg Body fat % = 16.63 / 62 × 100 = 26.8%

Example 3: Formula Comparison (Male, 85 kg, 180 cm)

Formula	LBM (kg)
Boer	65.05
James	63.28
Hume	60.75

Results vary between formulas because each was derived from a different study population. Use Boer as your baseline.

Frequently Asked Questions

Why is LBM more useful than total body weight? Total body weight doesn’t tell you what you’re made of. Two people at 80 kg may be entirely different physically — one lean and muscular, another with high body fat. LBM gives you insight into what drives your metabolism. Tracking LBM over time tells you whether you’re gaining muscle or losing it during a diet or training program.

Which formula should I use? For most adults, use Boer (1984). It performs well across a wide range of body compositions and heights. The James formula can give unreliable results in individuals with high BMI because the squared term amplifies errors. Hume is reliable but was derived from a relatively narrow clinical dataset.

How does LBM relate to my protein needs? Nutritionists commonly recommend 1.6–2.2 g of protein per kg of LBM per day for people doing resistance training. If your LBM is 60 kg, that’s 96–132 g of protein daily. Using LBM rather than total body weight prevents overestimation of protein needs in individuals with high body fat.

Can I increase my LBM? Yes. Progressive resistance training (weightlifting, bodyweight exercises) stimulates muscle protein synthesis and increases LBM over time. Adequate protein intake and caloric surplus (or maintenance calories) are also needed. Conversely, severe caloric restriction without resistance training typically causes loss of both fat and LBM.

Is LBM the same as muscle mass? No. LBM includes muscle but also bones, organs, connective tissue, blood, and water. Skeletal muscle mass alone is roughly 30–55% of total body weight in adults. You cannot separate these components with an anthropometric formula — only DXA scanning, bioelectrical impedance analysis (BIA), or similar techniques provide tissue-level breakdowns.