Lean Body Mass Calculator — Boer, James & Hume Formulas

What lean body mass actually measures

Bodyweight alone tells you how much you weigh. Lean body mass tells you how much of that weight is doing active metabolic work. LBM encompasses everything that is not fat: skeletal muscle, bone mineral, organ tissue, connective tissue, and body water. It is the compartment that drives your resting metabolic rate, responds to training, and sets a meaningful ceiling for how much protein you can usefully consume.

Understanding your LBM matters because two people with identical bodyweights and heights can have very different body compositions — and therefore different nutritional needs. A person with 20% body fat and another with 35% body fat will have the same BMI if they weigh the same, but their LBM values will differ by roughly 10 kg. That difference has real consequences for protein targets, calorie requirements, and how training adaptations should be interpreted.

How to use this calculator

Enter your bodyweight (kg or lb), height (cm or ft/in), and biological sex, then click the calculate button. The calculator applies all three established LBM formulas simultaneously and displays the results side by side. Boer is highlighted as the primary estimate; James and Hume are shown for reference. No result is displayed until all inputs have been filled.

Understanding the three LBM formulas

There are three established lean body weight formulas used to estimate LBM: Boer, James, and Hume — each derived from different populations and with different strengths.

Boer (1984) — primary result

Boer’s formula was derived from direct measurement data and has been subsequently validated across broad adult weight ranges, making it the most widely recommended for general-population use. The formula uses weight and height as predictors and applies different coefficients for males and females to account for typical differences in fat distribution and bone density.

• Male: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2
• Female: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3

The higher height coefficient in the female formula reflects the proportionally greater contribution of height to lean mass in women, where a larger fraction of LBM at a given weight is bone and connective tissue relative to muscle compared with males.

James (1976) — reference estimate

The James formula originated in a UK government report on obesity and was widely adopted in clinical pharmacokinetics for drug dosing calculations. It performs well across moderate weight ranges but is known to produce implausible (negative or near-zero) values at very high weight-to-height ratios — a recognised limitation of the formula.

• Male: LBM = 1.1 × weight(kg) − 128 × (weight(kg) / height(cm))²
• Female: LBM = 1.07 × weight(kg) − 148 × (weight(kg) / height(cm))²

If your James result is substantially lower than the Boer estimate, it may indicate that your weight-to-height ratio falls in the range where the James formula is less reliable. In this case, weight the Boer result more heavily.

Hume (1966) — reference estimate

Hume’s formula is one of the earliest published LBM equations and has a longer track record in the scientific literature than either James or Boer. It uses linear regression coefficients applied to weight and height, and tends to produce estimates that fall between the Boer and James values for most body sizes.

• Male: LBM = 0.3281 × weight(kg) + 0.3393 × height(cm) − 29.5336
• Female: LBM = 0.2969 × weight(kg) + 0.4165 × height(cm) − 43.2933

Using LBM to refine your protein target

The Protein Intake Calculator on NoGymLab uses total bodyweight as the default input, which is practical and accurate enough for most people within a normal body-fat range. For individuals whose body fat sits above roughly 30% or below 12%, using LBM as the denominator produces meaningfully more accurate targets.

Use the LBM chart below to apply LBM-based protein targets: take your Boer LBM result and multiply by the evidence-based range for your goal.

Goal	Multiplier	Example (55 kg LBM)
Fat loss	1.6–2.4 g/kg	88–132 g/day
Muscle gain	1.6–2.2 g/kg	88–121 g/day
Maintenance	1.2–1.6 g/kg	66–88 g/day

These ranges come from the ISSN position stand on protein and exercise (Jäger et al., 2017) and are the same ranges used in the Protein Intake Calculator.

A note on tracking LBM over time

Because these are anthropometric formulas derived from population-level regression equations, they carry an inherent estimation error of approximately ±2–3 kg. Small week-to-week changes in the output should not be interpreted as actual changes in lean tissue — they may simply reflect normal fluctuations in hydration, which affects bodyweight and therefore the formula inputs. LBM tracking is most meaningful over 8–12 week intervals, where genuine tissue changes can exceed the estimation noise.

Frequently asked questions

What is lean body mass?

Lean body mass is total bodyweight minus fat mass. It includes everything your body contains that is not adipose tissue — primarily skeletal muscle, bone, organs, skin, connective tissue, and body water. LBM is not the same as muscle mass alone; it is a broader measure that captures the metabolically active, non-fat portion of the body. For a person weighing 70 kg with 15% body fat, LBM would be approximately 59.5 kg.

Which LBM formula is most accurate?

No anthropometric formula matches the precision of a DEXA scan, which remains the clinical gold standard for body composition. Among the three formulas provided here, Boer (1984) is the primary recommendation — it was derived from a direct measurement dataset and has been validated across the widest range of body sizes. The James formula (1976) was historically used in clinical pharmacokinetics but tends to underestimate LBM in individuals at the upper end of the weight spectrum. The Hume formula (1966) is included as a reference point; it was one of the earliest height-weight LBM equations. Across typical adult body weights, the three formulas usually agree within ±1–2 kg.

How does lean body mass differ from fat-free mass?

The terms are often used interchangeably but are technically distinct. Fat-free mass (FFM) excludes all lipids, including essential structural fats in the nervous system and cell membranes. Lean body mass retains a small amount of essential fat (roughly 2–3% of bodyweight in males, 10–12% in females) on the grounds that this fat is physiologically necessary and cannot be mobilised during starvation. In practice, the difference between LBM and FFM is small for most adults, and the formulas in this calculator estimate LBM rather than FFM.

Why use LBM instead of total bodyweight for protein targets?

Total bodyweight includes fat mass, which has minimal protein requirements because adipose tissue is largely inactive metabolically. Using total bodyweight as the denominator therefore overestimates protein needs in individuals who carry high body fat, and slightly underestimates them in very lean individuals. For most people within a normal body-fat range, total bodyweight is a practical and sufficiently accurate basis for protein targets — which is why the Protein Intake Calculator on this site uses it by default. LBM-based targets become meaningfully more accurate at body-fat percentages above roughly 30% or below 12%.

What should I do with my LBM result?

The most immediate practical application is refining your protein intake target. If your goal is fat loss and your LBM is 55 kg, your evidence-based protein target is 55 × 1.6–2.4 g = 88–132 g per day, rather than the higher figure you would get using total bodyweight. LBM can also be tracked over time as a proxy for lean tissue changes during a training or diet programme — noting that anthropometric estimates carry an inherent measurement error of ±2–3 kg, so small changes should be interpreted cautiously.

Sources

1. Boer P (1984). Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology. PMID 6496691 DOI
2. Hume R (1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology. PMID 5965883 DOI
3. Janmahasatian S, Duffull SB, Ash S, Ward LC, Byrne NM, Green B (2005). Quantification of lean bodyweight. Clinical Pharmacokinetics. PMID 16176118 DOI
4. James WPT (1976). Research on obesity. HMSO, London.