{
  "slug": "power-to-weight",
  "title": "Power-to-Weight Ratio Calculator",
  "category": "Cycling",
  "category_slug": "cycling",
  "tier": 1,
  "summary": "Calculate watts per kilogram and compare against duration-specific performance bands",
  "description": "This calculator divides power output in watts by body weight in kilograms to produce a power-to-weight ratio (W/kg), then classifies the result using Coggan's duration-specific performance bands. It accepts power in watts, weight in kilograms, and a power-type selection (5-second sprint, 1-minute, 5-minute, or FTP/20-minute), then returns a W/kg figure and a performance category ranging from Untrained to World Class. The classification bands are duration-dependent: a 6 W/kg sprint represents recreational ability, whereas the same ratio sustained for 20 minutes indicates elite-level endurance.",
  "page_url": "https://fitmetriclab.com/en/tools/cycling/power-to-weight/",
  "api_url": "https://fitmetriclab.com/api/tools/power-to-weight.json",
  "formula": {
    "id": "power_to_weight",
    "expression": "\\text{W/kg} = \\frac{P}{w}",
    "variables": [
      {
        "symbol": "P",
        "description": "Power in watts"
      },
      {
        "symbol": "w",
        "description": "Weight in kg"
      },
      {
        "symbol": "\\tau",
        "description": "Power-type effort (e.g. FTP, 5\\text{-}min)"
      }
    ]
  },
  "inputs": [
    {
      "id": "watts",
      "label": "Power",
      "type": "number",
      "unit": "W",
      "default": 200,
      "min": 1,
      "max": 2000,
      "step": 1
    },
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 20,
      "max": 300,
      "step": 0.1
    },
    {
      "id": "power_type",
      "label": "Power Type",
      "type": "select",
      "unit": null,
      "default": "ftp",
      "options": [
        {
          "value": "ftp",
          "label": "FTP (20-min)"
        },
        {
          "value": "5min",
          "label": "5-minute"
        },
        {
          "value": "1min",
          "label": "1-minute"
        },
        {
          "value": "sprint",
          "label": "5-second sprint"
        }
      ]
    }
  ],
  "worked_example": {
    "inputs": {
      "watts": 200,
      "weight_kg": 75,
      "power_type": "ftp"
    },
    "expected_output": "2.67 W/kg"
  },
  "result_summary_template": "At {watts} watts of power and {weight_kg} kg body weight, power-to-weight ratio is {result}.",
  "methodology": "Divides power (watts) by body mass (kg) to yield W/kg, then applies duration-specific classification bands from Coggan's power-profile chart. FTP (20-min) bands: 2.0–3.2–4.0–5.0–6.4+ W/kg; sprint (5-sec) bands: 8.0–12.0–15.0–18.0–21.0+ W/kg. Categories: Untrained, Recreational, Trained, Competitive, Elite, World Class.",
  "sources": [
    {
      "label": "Coggan AR. Training and Racing Using a Power Meter. VeloPress. 2006.",
      "url": "https://www.velopress.com/"
    },
    {
      "label": "Jeukendrup AE, Craig NP, Hawley JA. The bioenergetics of world class cycling. Journal of Science and Medicine in Sport. 2000;3(4):414-433.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/11235007/"
    },
    {
      "label": "Padilla S, Mujika I, Angulo F, Goiriena JJ. Scientific approach to the 1-h cycling world record: a case study. Journal of Applied Physiology. 2000;89(4):1522-1527.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/11007590/"
    }
  ],
  "faqs": [
    {
      "question": "Why do sprint and FTP thresholds differ so much?",
      "answer": "Shorter efforts recruit more fast-twitch muscle fibers and draw on anaerobic pathways, producing higher peak watts. A 20-minute FTP effort relies on sustained aerobic capacity, yielding lower absolute power. The classification bands scale accordingly: 6 W/kg for 5 seconds is recreational, while 6 W/kg for 20 minutes is world-class."
    },
    {
      "question": "Does body weight include the bike?",
      "answer": "No. Power-to-weight ratio uses rider body mass only. Total system weight (rider plus bike) matters for climbing speed, but the W/kg performance metric isolates physiological output per kilogram of body mass to allow peer comparison."
    },
    {
      "question": "Are these bands the same for men and women?",
      "answer": "The bands derive from mixed-population data and tend to reflect male power profiles. Elite women often achieve equivalent climbing performance at lower absolute W/kg values due to differences in body composition and aerodynamics. Gender-specific bands exist in some coaching literature but are not universally standardized."
    },
    {
      "question": "Can power-to-weight predict time-trial performance?",
      "answer": "Power-to-weight is less predictive on flat courses where aerodynamic drag dominates. Absolute watts, frontal area, and CdA (drag coefficient × area) become more important. On climbs steeper than 7%, W/kg correlates strongly with speed because gravity resistance outweighs air resistance."
    },
    {
      "question": "How often should power and weight be remeasured?",
      "answer": "Power output fluctuates with training state, fatigue, and testing protocol. Body mass varies daily with hydration and glycogen stores. Testing FTP every 4–8 weeks and weighing under consistent conditions (morning, fasted) reduces measurement noise. Power-meter zero-offset calibration before each ride improves data reliability."
    }
  ],
  "related_tools": [
    {
      "slug": "cycling-power",
      "title": "Cycling Power Calculator (Watts from Speed)",
      "api_url": "https://fitmetriclab.com/api/tools/cycling-power.json",
      "page_url": "https://fitmetriclab.com/en/tools/cycling/cycling-power/"
    },
    {
      "slug": "cycling-power-zones",
      "title": "Cycling Power Zones Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/cycling-power-zones.json",
      "page_url": "https://fitmetriclab.com/en/tools/cycling/cycling-power-zones/"
    },
    {
      "slug": "gear-ratio",
      "title": "Bike Gear Ratio Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/gear-ratio.json",
      "page_url": "https://fitmetriclab.com/en/tools/cycling/gear-ratio/"
    }
  ],
  "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."
}