{
  "slug": "body-fat",
  "title": "Body Fat Calculator",
  "heading": "Body Fat Percentage Calculator",
  "category": "fitness-health",
  "url": "https://www.revenuelab.fyi/toolbox/body-fat",
  "summary": "U.S. Navy method for body fat percentage.",
  "description": "Uses the U.S. Navy circumference method (neck, waist, hips for women) to estimate body fat percent.",
  "formula": null,
  "dateModified": "2026-10-03",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=body-fat",
  "inputs": [
    {
      "id": "units",
      "label": "Units",
      "kind": "select",
      "hint": null,
      "default": "imperial",
      "options": [
        {
          "value": "metric",
          "label": "Metric (kg, cm)"
        },
        {
          "value": "imperial",
          "label": "Imperial (lb, in)"
        }
      ]
    },
    {
      "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": null,
      "min": 0,
      "max": null
    },
    {
      "id": "neck",
      "label": "Neck circumference",
      "kind": "number",
      "hint": null,
      "default": 15,
      "unit": null,
      "min": 0,
      "max": null
    },
    {
      "id": "waist",
      "label": "Waist circumference",
      "kind": "number",
      "hint": null,
      "default": 34,
      "unit": null,
      "min": 0,
      "max": null
    },
    {
      "id": "hip",
      "label": "Hip (women only)",
      "kind": "number",
      "hint": null,
      "default": 38,
      "unit": null,
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "bf",
      "label": "Body fat",
      "format": "percent",
      "hint": null,
      "primary": true
    }
  ],
  "worked_example": {
    "inputs": [
      "Units: Imperial (lb, in)",
      "Sex: Male",
      "Height: 70",
      "Neck circumference: 15",
      "Waist circumference: 34",
      "Hip (women only): 38"
    ],
    "outputs": [
      "Body fat: 17.4%"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter units.",
      "Enter sex.",
      "Enter height.",
      "Enter neck circumference.",
      "Enter waist circumference.",
      "Enter hip (women only).",
      "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": {
        "units": "imperial",
        "sex": "male",
        "height": 70,
        "neck": 9,
        "waist": 20.4,
        "hip": 22.8
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "units": "imperial",
        "sex": "male",
        "height": 70,
        "neck": 15,
        "waist": 34,
        "hip": 38
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "units": "imperial",
        "sex": "male",
        "height": 70,
        "neck": 24,
        "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 body fat percentage calculator work?",
      "a": "Uses the U.S. Navy circumference method (neck, waist, hips for women) to estimate body fat percent."
    },
    {
      "q": "What do I need to enter?",
      "a": "6 values: units, sex, height, neck circumference, waist circumference, and hip (women only). 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/bmi",
    "https://www.revenuelab.fyi/toolbox/ideal-weight",
    "https://www.revenuelab.fyi/toolbox/tdee"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Body Fat Calculator (https://www.revenuelab.fyi/toolbox/body-fat)"
}