{
  "slug": "bmi-calculator",
  "title": "BMI Calculator",
  "category": "Body Composition",
  "category_slug": "body-composition",
  "tier": 1,
  "summary": "Calculate Body Mass Index from weight and height using the standard kg/m² formula.",
  "description": "This calculator computes Body Mass Index (BMI) using the standard Quetelet equation: weight in kilograms divided by height in meters squared (kg/m²). It requires weight and height as inputs and returns a single numerical BMI value that represents the ratio of mass to stature. BMI is a population-level screening metric; it does not measure body composition directly and may misclassify individuals with high muscle mass or varying body proportions.",
  "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmi-calculator/",
  "api_url": "https://fitmetriclab.com/api/tools/bmi-calculator.json",
  "formula": {
    "id": "bmi",
    "expression": "\\text{BMI} = \\frac{w}{h^{2}}",
    "variables": [
      {
        "symbol": "w",
        "description": "Weight in kg"
      },
      {
        "symbol": "h",
        "description": "Height in metres"
      }
    ]
  },
  "inputs": [
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 20,
      "max": 300,
      "step": 0.1
    },
    {
      "id": "height_cm",
      "label": "Height",
      "type": "number",
      "unit": "cm",
      "default": 175,
      "min": 100,
      "max": 230,
      "step": 0.5
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 75,
      "height_cm": 175
    },
    "expected_output": "24.5"
  },
  "result_summary_template": "At {height_cm} cm tall and weighing {weight_kg} kg, the Body Mass Index calculation yields {result}.",
  "methodology": "Body Mass Index = weight in kilograms divided by height in meters squared (kg/m²). The formula was first described by Adolphe Quetelet in 1832 and later standardized by Ancel Keys in 1972 under the name 'body mass index.' Height in centimeters is converted to meters before squaring.",
  "sources": [
    {
      "label": "Keys A, et al. Indices of relative weight and obesity. J Chronic Dis. 1972;25(6):329-343.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/4650929/"
    },
    {
      "label": "World Health Organization. Physical status: the use and interpretation of anthropometry. WHO Technical Report Series 854. 1995.",
      "url": "https://www.who.int/publications/i/item/9241208546"
    },
    {
      "label": "National Heart, Lung, and Blood Institute. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication 98-4083. 1998.",
      "url": "https://www.nhlbi.nih.gov/files/docs/guidelines/ob_gdlns.pdf"
    }
  ],
  "faqs": [
    {
      "question": "What does BMI measure?",
      "answer": "BMI quantifies the ratio of weight to height squared. It does not directly measure body fat percentage, lean mass, or fat distribution. The metric was designed for population-level epidemiological research, not individual body-composition assessment."
    },
    {
      "question": "Why might BMI be inaccurate for athletes?",
      "answer": "Muscle tissue is denser than adipose tissue. Individuals with above-average muscle mass—powerlifters, sprinters, bodybuilders—often register BMI values in ranges typically associated with overweight or obese populations, despite low body fat percentages. The formula does not account for tissue composition."
    },
    {
      "question": "Can two people with the same BMI have different body compositions?",
      "answer": "Yes. BMI reflects only weight and height. Two individuals with identical BMI values may have markedly different percentages of fat mass, muscle mass, bone density, and visceral adiposity. Body-composition methods like DEXA, hydrostatic weighing, or skinfold calipers provide more granular data."
    },
    {
      "question": "How often was BMI intended to be calculated?",
      "answer": "BMI was developed as a cross-sectional screening tool for large populations. Frequent recalculation is not inherent to the metric's design. Tracking trends over months or years may provide more context than single measurements, though body-composition tools offer more actionable feedback."
    },
    {
      "question": "What are the standard BMI classification ranges?",
      "answer": "The World Health Organization defines underweight as <18.5, normal weight as 18.5–24.9, overweight as 25.0–29.9, and obese as ≥30.0 kg/m². These thresholds were derived from Western population studies and may not generalize across all ethnic groups or activity levels."
    }
  ],
  "related_tools": [
    {
      "slug": "bmr-mifflin",
      "title": "BMR Calculator (Mifflin-St Jeor)",
      "api_url": "https://fitmetriclab.com/api/tools/bmr-mifflin.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmr-mifflin/"
    },
    {
      "slug": "tdee-calculator",
      "title": "TDEE Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/tdee-calculator.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/tdee-calculator/"
    },
    {
      "slug": "bmr-harris-benedict",
      "title": "BMR Calculator (Harris-Benedict)",
      "api_url": "https://fitmetriclab.com/api/tools/bmr-harris-benedict.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmr-harris-benedict/"
    }
  ],
  "last_updated": "2026-04-22",
  "price": {
    "value": 0,
    "currency": "USD"
  },
  "runs_in_browser": true,
  "disclaimer": "Educational estimate produced from a published formula. Not medical, nutritional, or training advice. Calculations are deterministic — apply the formula to the inputs to reproduce the result."
}