{
    "name": "Lean Body Mass Calculator",
    "url": "https://calculators.geekmidst.com/calculators/lean-body-mass-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/lean-body-mass-calculator.md",
    "category": "Health & fitness",
    "description": "Estimate lean body mass from height, weight and sex with the Boer and Hume equations, or from a measured body fat percentage if you have one.",
    "summary": "Lean body mass is everything except fat: muscle, bone, organs and water. The Boer and Hume equations estimate it from height and weight; a measured body fat percentage gives a more direct figure.",
    "also_called": [
        "LBM calculator",
        "Fat-free mass calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "sex",
            "label": "Sex",
            "type": "segmented",
            "default": "male",
            "options": {
                "female": "Female",
                "male": "Male"
            }
        },
        {
            "name": "units",
            "label": "Units",
            "type": "segmented",
            "default": "metric",
            "options": {
                "metric": "Metric (cm, kg)",
                "us": "US (ft, in, lb)"
            }
        },
        {
            "name": "height_cm",
            "label": "Height",
            "type": "number",
            "default": "180",
            "unit": "cm",
            "shown_when": {
                "units": "metric"
            }
        },
        {
            "name": "weight_kg",
            "label": "Weight",
            "type": "number",
            "default": "80",
            "unit": "kg",
            "shown_when": {
                "units": "metric"
            }
        },
        {
            "name": "height_ft",
            "label": "Height (feet)",
            "type": "number",
            "default": "5",
            "unit": "ft",
            "shown_when": {
                "units": "us"
            }
        },
        {
            "name": "height_in",
            "label": "Height (inches)",
            "type": "number",
            "default": "11",
            "unit": "in",
            "optional": true,
            "shown_when": {
                "units": "us"
            }
        },
        {
            "name": "weight_lb",
            "label": "Weight",
            "type": "number",
            "default": "176",
            "unit": "lb",
            "shown_when": {
                "units": "us"
            }
        },
        {
            "name": "body_fat",
            "label": "Body fat (optional)",
            "type": "number",
            "default": "",
            "unit": "%",
            "optional": true
        }
    ],
    "outputs": [
        {
            "key": "boer",
            "label": "Lean body mass (Boer)",
            "format": "number"
        },
        {
            "key": "hume",
            "label": "Lean body mass (Hume)",
            "format": "number"
        },
        {
            "key": "lean_pct",
            "label": "Lean share of weight (Boer)",
            "format": "percent"
        },
        {
            "key": "fat_mass",
            "label": "Implied fat mass (Boer)",
            "format": "number"
        },
        {
            "key": "from_body_fat",
            "label": "From your body fat %",
            "format": "text"
        }
    ],
    "formula": {
        "text": "Boer: men 0.407W + 0.267H − 19.2, women 0.252W + 0.473H − 48.3;  Hume: men 0.32810W + 0.33929H − 29.5336, women 0.29569W + 0.41813H − 43.2933;  From body fat: W × (1 − BF%)",
        "variables": {
            "W": "weight in kg",
            "H": "height in cm",
            "BF%": "measured body fat percentage"
        }
    },
    "worked_example": {
        "inputs": {
            "sex": "male",
            "units": "metric",
            "height_cm": "180",
            "weight_kg": "80",
            "height_ft": "5",
            "height_in": "11",
            "weight_lb": "176",
            "body_fat": ""
        },
        "steps": [
            "Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg.",
            "Hume: 0.3281 × 80 + 0.33929 × 180 − 29.5336 = 26.25 + 61.07 − 29.53 = 57.8 kg.",
            "Lean share (Boer) = 61.42 ÷ 80 = 76.8%, implying 18.6 kg of fat."
        ],
        "result": "A man 180 cm tall weighing 80 kg has an estimated lean body mass of about 61.4 kg (Boer) or 57.8 kg (Hume)."
    },
    "interpretation": "The two equations differ by a few kilograms, which shows the uncertainty of height-and-weight estimates. Lean body mass is used to scale protein targets, to dose some medicines and contrast agents, and to follow changes in muscle during training or weight loss.",
    "assumptions": [
        "Adult equations; Boer (1984) and Hume (1966) were derived in adult populations.",
        "Weight in kg and height in cm (US inputs are converted)."
    ],
    "limitations": [
        "Height-and-weight equations cannot tell a muscular person from a person with more fat at the same size.",
        "Accuracy falls in obesity, in older adults and in children."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Is lean body mass the same as muscle mass?",
            "answer": "No. It includes bone, organs, skin and body water as well as muscle, so it is always larger than muscle mass alone."
        },
        {
            "question": "Which result should I use?",
            "answer": "If you have a reliable body fat measurement, the body-fat method is the most direct. Otherwise Boer is the equation most often used clinically."
        }
    ],
    "sources": [
        {
            "title": "Wikipedia: Lean body mass (Boer and Hume equations, with primary citations)",
            "url": "https://en.wikipedia.org/wiki/Lean_body_mass"
        }
    ],
    "related": [
        {
            "name": "Body Fat Calculator",
            "url": "https://calculators.geekmidst.com/calculators/body-fat-calculator"
        },
        {
            "name": "Ideal Weight Calculator",
            "url": "https://calculators.geekmidst.com/calculators/ideal-weight-calculator"
        },
        {
            "name": "BMI Calculator",
            "url": "https://calculators.geekmidst.com/calculators/bmi-calculator"
        },
        {
            "name": "BMR Calculator",
            "url": "https://calculators.geekmidst.com/calculators/bmr-calculator"
        }
    ],
    "disclaimer": "This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.",
    "publisher": "GM¹X CalcVerse"
}