{
  "id": "lean-body-mass",
  "version": "c69efd4c658f",
  "status": "published",
  "name": "Lean Body Mass Calculator",
  "question": "What is my lean body mass?",
  "summary": "Estimates lean body mass (everything but fat) from sex, height and weight by the Boer, James and Hume formulas, with the body fat percentage it implies.",
  "category": "health",
  "subcategory": "body",
  "url": "https://www.acalculator.org/health/lean-body-mass-calculator",
  "markdown": "https://www.acalculator.org/health/lean-body-mass-calculator.md",
  "kind": "function",
  "method": "Boer: men 0.407W + 0.267H − 19.2, women 0.252W + 0.473H − 48.3; James: men 1.1W − 128(W/H)², women 1.07W − 148(W/H)²; Hume: men 0.32810W + 0.33929H − 29.5336, women 0.29569W + 0.41813H − 43.2933 (W in kg, H in cm).",
  "assumptions": [
    "The formulas are for adults. They estimate lean mass from height and weight only, not from a body scan.",
    "Body fat is the weight minus the Boer lean mass, as a percent of the weight.",
    "Height from 1 to 2.5 m (3 ft 3 in to 8 ft 2 in) and weight from 25 to 350 kg (55 to 772 lb)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "sex": {
        "title": "Sex",
        "description": "Sex at birth, which the body formulas use.",
        "type": "string",
        "enum": [
          "male",
          "female"
        ]
      },
      "height": {
        "title": "Height",
        "description": "Your height without shoes.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 1,
        "maximum": 2.5
      },
      "weight": {
        "title": "Weight",
        "description": "Your body weight.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 25,
        "maximum": 350
      }
    }
  },
  "outputs": {
    "boer": {
      "label": "Lean body mass (Boer)",
      "description": "Lean body mass by the Boer (1984) formula, in pounds.",
      "format": "number"
    },
    "boerKg": {
      "label": "Lean body mass, Boer (kg)",
      "description": "Lean body mass by the Boer formula, in kilograms.",
      "format": "number"
    },
    "fat": {
      "label": "Body fat (Boer)",
      "description": "The part of your weight that is not lean mass by Boer: (weight − LBM) ÷ weight.",
      "format": "percent"
    },
    "james": {
      "label": "Lean body mass (James)",
      "description": "Lean body mass by the James (1976) formula, in pounds; left out past the weight where it peaks.",
      "format": "number"
    },
    "jamesKg": {
      "label": "Lean body mass, James (kg)",
      "description": "Lean body mass by the James formula, in kilograms.",
      "format": "number"
    },
    "hume": {
      "label": "Lean body mass (Hume)",
      "description": "Lean body mass by the Hume (1966) formula, in pounds.",
      "format": "number"
    },
    "humeKg": {
      "label": "Lean body mass, Hume (kg)",
      "description": "Lean body mass by the Hume formula, in kilograms.",
      "format": "number"
    },
    "note": {
      "label": "About the James formula",
      "description": "Why the James result is left out, when it is.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "sex": "male",
      "height": "5ft10in",
      "weight": "180lb"
    },
    "outputs": {
      "boer": 135.6,
      "boerKg": 61.5,
      "fat": 24.7,
      "james": 138.5,
      "jamesKg": 62.8,
      "hume": 126.9,
      "humeKg": 57.6
    },
    "text": "At 5 ft 10 in and 180 lb, your lean body mass is about 135.6 lb by the Boer formula."
  },
  "examples": [
    {
      "given": {
        "sex": "male",
        "height": 1.778,
        "weight": 81.6466266
      },
      "expect": {
        "boerKg": 61.5,
        "boer": 135.6,
        "fat": 24.7,
        "humeKg": 57.6,
        "hume": 126.9,
        "jamesKg": 62.8,
        "james": 138.5
      },
      "source": "hand calculation in content.mdx: Boer 0.407 × 81.6466266 + 0.267 × 177.8 − 19.2 = 61.5028…; De Cassai A et al., Regional anesthesia in obese patients, Saudi J Anaesth 2025, lean body mass table: Boer, James and Hume formulas, height in cm, weight in kg (https://europepmc.org/article/PMC/PMC12007849, retrieved 2026-10-02)"
    },
    {
      "given": {
        "sex": "female",
        "height": 1.65,
        "weight": 60
      },
      "expect": {
        "boerKg": 44.9,
        "boer": 98.9,
        "fat": 25.2,
        "jamesKg": 44.6,
        "humeKg": 43.4
      },
      "source": "hand calculation in content.mdx: Boer 0.252 × 60 + 0.473 × 165 − 48.3 = 44.865; De Cassai A et al., Regional anesthesia in obese patients, Saudi J Anaesth 2025, lean body mass table: Boer, James and Hume formulas, height in cm, weight in kg (https://europepmc.org/article/PMC/PMC12007849, retrieved 2026-10-02); Caruso D et al., Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula, BioMed Res Int 2018 (https://europepmc.org/article/PMC/PMC6110034, retrieved 2026-10-02)"
    },
    {
      "given": {
        "sex": "male",
        "height": 1.7,
        "weight": 130
      },
      "expect": {
        "boerKg": 79.1,
        "humeKg": 70.8,
        "note": "The James formula is left out: above 124.2 kg at your height and sex it gives less lean mass for more weight, which is not realistic."
      },
      "source": "hand calculation in content.mdx: Boer 0.407 × 130 + 0.267 × 170 − 19.2 = 79.1; Caruso D et al., Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula, BioMed Res Int 2018 (https://europepmc.org/article/PMC/PMC6110034, retrieved 2026-10-02)"
    }
  ],
  "sources": [
    "De Cassai A, Zarantonello F, Pistollato E, et al. Regional anesthesia in obese patients: Challenges, considerations, and solutions. Saudi J Anaesth. 2025. Table: Boer, James and Hume lean body mass formulas for men and women (height in cm, weight in kg), retrieved 2026-10-02. https://europepmc.org/article/PMC/PMC12007849",
    "Caruso D, De Santis D, Rivosecchi F, et al. Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula. BioMed Res Int. 2018;2018:8521893 (Boer and James formulas), retrieved 2026-10-02. https://europepmc.org/article/PMC/PMC6110034",
    "Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632–F636 (abstract), retrieved 2026-10-02. https://europepmc.org/article/MED/6496691"
  ],
  "related": [
    "body-fat",
    "bmi",
    "ffmi",
    "ideal-weight"
  ],
  "changelog": []
}