{
    "name": "Body Fat Calculator",
    "url": "https://calculators.geekmidst.com/calculators/body-fat-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/body-fat-calculator.md",
    "category": "Health & fitness",
    "description": "Estimate body fat percentage from height, neck, waist and (for women) hip measurements with the US Navy circumference equations, plus fat and lean mass.",
    "summary": "The US Navy method estimates body fat from a few tape measurements and your height. It needs only a flexible tape and gives fat mass and lean mass alongside the percentage.",
    "also_called": [
        "Navy body fat calculator",
        "Body fat percentage 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 (in, lb)"
            }
        },
        {
            "name": "height",
            "label": "Height",
            "type": "number",
            "default": "178"
        },
        {
            "name": "neck",
            "label": "Neck",
            "type": "number",
            "default": "38"
        },
        {
            "name": "waist",
            "label": "Waist",
            "type": "number",
            "default": "86"
        },
        {
            "name": "hip",
            "label": "Hip",
            "type": "number",
            "default": "100",
            "shown_when": {
                "sex": "female"
            }
        },
        {
            "name": "weight_kg",
            "label": "Weight",
            "type": "number",
            "default": "80",
            "unit": "kg",
            "shown_when": {
                "units": "metric"
            }
        },
        {
            "name": "weight_lb",
            "label": "Weight",
            "type": "number",
            "default": "176",
            "unit": "lb",
            "shown_when": {
                "units": "us"
            }
        }
    ],
    "outputs": [
        {
            "key": "body_fat",
            "label": "Body fat",
            "format": "percent"
        },
        {
            "key": "fat_mass",
            "label": "Fat mass (kg or lb)",
            "format": "number"
        },
        {
            "key": "lean_mass",
            "label": "Lean mass (kg or lb)",
            "format": "number"
        }
    ],
    "formula": {
        "text": "Men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76;  Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387  (all in inches)",
        "variables": {
            "waist, neck, hip": "circumferences in inches (cm ÷ 2.54)",
            "height": "standing height in inches"
        }
    },
    "worked_example": {
        "inputs": {
            "sex": "male",
            "units": "metric",
            "height": "178",
            "neck": "38",
            "waist": "86",
            "hip": "",
            "weight_kg": "80",
            "weight_lb": "176"
        },
        "steps": [
            "Convert to inches: height 178 ÷ 2.54 = 70.08, neck 14.96, waist 33.86; waist − neck = 18.90.",
            "86.010 × log10(18.90) = 86.010 × 1.2765 = 109.79.",
            "70.041 × log10(70.08) = 70.041 × 1.8456 = 129.27.",
            "%BF = 109.79 − 129.27 + 36.76 = 17.3%. Fat mass = 80 × 0.173 ≈ 13.8 kg; lean mass ≈ 66.2 kg."
        ],
        "result": "A man 178 cm tall with a 38 cm neck and 86 cm waist has an estimated 17.3% body fat: about 13.8 kg of fat and 66.2 kg of lean mass at 80 kg."
    },
    "interpretation": "Use the result to follow a trend: measure the same way, at the same time of day, every few weeks. A change of a percentage point or two between single measurements is within the method’s error. Waist size on its own is also a useful health marker.",
    "assumptions": [
        "US Navy circumference equations (Hodgdon and Beckett, Naval Health Research Center, 1984), developed on adult military personnel.",
        "Measurements taken with a non-stretch tape, snug but not compressing the skin."
    ],
    "limitations": [
        "For an individual, results can differ from laboratory methods (such as DXA) by several percentage points.",
        "Less reliable for very lean, very muscular or very large bodies, older adults and pregnancy.",
        "Not a diagnosis; there is no single agreed set of healthy body-fat cut-offs, so none is shown."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Is this the same as the Army tape test?",
            "answer": "The Navy two- and three-site equations were used by several US services, but the US Army replaced its tape test with a waist-to-height ratio in July 2026. See the Army Body Composition Calculator for the current Army check."
        },
        {
            "question": "Why do women need a hip measurement?",
            "answer": "Women carry more fat around the hips and thighs, so the female equation adds the hip circumference to improve the estimate."
        }
    ],
    "sources": [
        {
            "title": "LibreTexts: The U.S. Navy body fat estimation formula",
            "url": "https://med.libretexts.org/Courses/Irvine_Valley_College/Physiology_Labs_at_Home/03:_Anthropometrics/3.02:_Part_B-_Circumference_Measures/3.2.04:_Part_B4-_The_U.S._Navy_body_fat_estimation_formula"
        }
    ],
    "related": [
        {
            "name": "Lean Body Mass Calculator",
            "url": "https://calculators.geekmidst.com/calculators/lean-body-mass-calculator"
        },
        {
            "name": "Army Body Composition Calculator",
            "url": "https://calculators.geekmidst.com/calculators/army-body-fat-calculator"
        },
        {
            "name": "BMI Calculator",
            "url": "https://calculators.geekmidst.com/calculators/bmi-calculator"
        },
        {
            "name": "Healthy Weight Calculator",
            "url": "https://calculators.geekmidst.com/calculators/healthy-weight-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"
}