{
  "slug": "body-fat-navy",
  "title": "Navy Body Fat Calculator",
  "heading": "Navy Method Body Fat Calculator",
  "category": "fitness-health",
  "url": "https://www.revenuelab.fyi/toolbox/body-fat-navy",
  "summary": "Body fat percentage from tape measurements.",
  "description": "The US Navy circumference method estimates body fat from neck, waist, and (for women) hip measurements. It is within a few points of DEXA for most people and free.",
  "formula": "Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=body-fat-navy",
  "inputs": [
    {
      "id": "sex",
      "label": "Sex",
      "kind": "select",
      "hint": null,
      "default": "male",
      "options": [
        {
          "value": "male",
          "label": "Male"
        },
        {
          "value": "female",
          "label": "Female"
        }
      ]
    },
    {
      "id": "height",
      "label": "Height",
      "kind": "number",
      "hint": null,
      "default": 70,
      "unit": "in",
      "min": 48,
      "max": 84
    },
    {
      "id": "weight",
      "label": "Weight",
      "kind": "number",
      "hint": null,
      "default": 185,
      "unit": "lb",
      "min": 60,
      "max": 500
    },
    {
      "id": "neck",
      "label": "Neck",
      "kind": "number",
      "hint": null,
      "default": 15.5,
      "unit": "in",
      "min": 8,
      "max": 30
    },
    {
      "id": "waist",
      "label": "Waist",
      "kind": "number",
      "hint": null,
      "default": 34,
      "unit": "in",
      "min": 18,
      "max": 80
    },
    {
      "id": "hip",
      "label": "Hip (women)",
      "kind": "number",
      "hint": null,
      "default": 38,
      "unit": "in",
      "min": 20,
      "max": 80
    }
  ],
  "outputs": [
    {
      "id": "bf",
      "label": "Body fat",
      "format": "percent",
      "hint": null,
      "primary": true
    },
    {
      "id": "category",
      "label": "Category",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "fatMass",
      "label": "Fat mass (lb)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "lean",
      "label": "Lean mass (lb)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "toTen",
      "label": "Pounds to lose for a lean target",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "bmi",
      "label": "BMI for reference",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Sex: Male",
      "Height: 70 in",
      "Weight: 185 lb",
      "Neck: 15.5 in",
      "Waist: 34 in",
      "Hip (women): 38 in"
    ],
    "outputs": [
      "Body fat: 16.5%",
      "Category: Fitness",
      "Fat mass (lb): 30.6",
      "Lean mass (lb): 154.4",
      "Pounds to lose for a lean target: 13.4",
      "BMI for reference: 26.5"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter sex.",
      "Enter height (in).",
      "Enter weight (lb).",
      "Enter neck (in).",
      "Enter waist (in).",
      "Enter hip (women) (in).",
      "Read your body fat on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "sex": "male",
        "height": 70,
        "weight": 185,
        "neck": 9.299999999999999,
        "waist": 20.4,
        "hip": 22.8
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "sex": "male",
        "height": 70,
        "weight": 185,
        "neck": 15.5,
        "waist": 34,
        "hip": 38
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "sex": "male",
        "height": 70,
        "weight": 185,
        "neck": 24.8,
        "waist": 54.400000000000006,
        "hip": 60.800000000000004
      }
    }
  ],
  "limitations": [
    "Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.",
    "Results do not account for medical conditions, medication, or pregnancy.",
    "Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it."
  ],
  "faq": [
    {
      "q": "How does the navy method body fat calculator work?",
      "a": "The US Navy circumference method estimates body fat from neck, waist, and (for women) hip measurements. It is within a few points of DEXA for most people and free. The underlying maths is: Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76."
    },
    {
      "q": "What do I need to enter?",
      "a": "6 values: sex, height, weight, neck, waist, and hip (women). Each field starts with a sensible default, so you can change one number at a time and watch the result move."
    },
    {
      "q": "What does the body fat result mean?",
      "a": "It is returned as a percentage and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds."
    },
    {
      "q": "Is this calculator free, and do I need an account?",
      "a": "Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser."
    },
    {
      "q": "How accurate is the result?",
      "a": "It applies the standard formula exactly, so the arithmetic is precise. Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for anyone tracking a health or training target and wanting the standard formula applied correctly, without a signup or an app."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/calorie-deficit",
    "https://www.revenuelab.fyi/toolbox/protein-intake",
    "https://www.revenuelab.fyi/toolbox/ideal-weight"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Navy Body Fat Calculator (https://www.revenuelab.fyi/toolbox/body-fat-navy)"
}