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Lean Body Mass Calculator
Estimates lean body mass (fat-free mass) from weight, height and sex with the Boer (1984), James (1976) and Hume (1966) formulas.
When to use
You need fat-free mass for drug dosing, nutrition planning or as a body-composition reference without a scan.
Do not use when: You have measured body-fat percentage (lean mass = weight × (1 − body fat) is then more accurate) or the person is a child.
Formula
Boer: male 0.407·W + 0.267·H − 19.2, female 0.252·W + 0.473·H − 48.3. James: male 1.1·W − 128·(W/H)², female 1.07·W − 148·(W/H)². Hume: male 0.32810·W + 0.33929·H − 29.5336, female 0.29569·W + 0.41813·H − 43.2933. W in kg, H in cm.
Inputs
| Parameter | Type | Unit | Required | Description |
|---|---|---|---|---|
sex | enum: male | female | yes | Biological sex used to select the formula coefficients. | |
weight_kg | number | kg | yes | Body weight in kilograms. Range: > 0, ≤ 700 |
height_cm | number | cm | yes | Height in centimetres. Range: ≥ 50, ≤ 300 |
Outputs
| Output | Type | Unit | Description |
|---|---|---|---|
boer_kg | number | kg | Boer (1984) formula, commonly used for anaesthetic dosing. |
james_kg | number | kg | James (1976) formula. |
hume_kg | number | kg | Hume (1966) formula. |
boer_body_fat_percent | number | % | 100 × (1 − boer_kg / weight_kg). |
Example
Male, 70 kg, 175 cm: {"sex":"male","weight_kg":70,"height_cm":175} → {"boer_kg":56,"james_kg":56.5,"hume_kg":52.8,"boer_body_fat_percent":20}
Female, 60 kg, 165 cm: {"sex":"female","weight_kg":60,"height_cm":165} → {"boer_kg":44.9,"james_kg":44.6,"hume_kg":43.4}
GET https://tttkmbb.com/api/v1/calculate/lean-body-mass?sex=male&weight_kg=70&height_cm=175
Machine access
- API:
GET https://tttkmbb.com/api/v1/calculate/lean-body-mass(query parameters) orPOSTwith a JSON body{"inputs": {...}} - Schema: https://tttkmbb.com/api/v1/calculators/lean-body-mass · Markdown: https://tttkmbb.com/health/lean-body-mass.md · JSON definition: https://tttkmbb.com/health/lean-body-mass.json
- MCP: server
https://tttkmbb.com/mcp, toolrun_calculator with calculator_id="lean-body-mass" - OpenAPI operationId:
calculate_lean_body_mass - Freshness:
static. Authentication: none. Rate limit: fair use (see rate limits).
Sources
FAQ
Which formula should I use?
Boer is the most common in clinical dosing; James overestimates in obesity; Hume is older. Differences of 2–4 kg are typical.
Related calculators
- Body Fat Calculator — Measure-based body fat and lean mass.