{
  "slug": "watts-to-mets",
  "title": "Watts to METs Converter",
  "category": "Conversions",
  "category_slug": "conversions",
  "tier": 2,
  "summary": "Convert cycling power output into METs and oxygen uptake using the ACSM leg-ergometry equation.",
  "description": "This converter turns a cycling power output in watts into a MET value using the ACSM metabolic equation for leg ergometry. It first estimates oxygen uptake — VO₂ in ml/kg/min — from the work rate and body mass, then divides by the resting reference of 3.5 ml/kg/min to express the effort in METs. The result also includes the calorie-per-hour figure that MET value implies at your body weight. The equation was derived for steady-state stationary cycling, so treat outputs for other modalities as approximations at best.",
  "page_url": "https://fitmetriclab.com/en/tools/conversions/watts-to-mets/",
  "api_url": "https://fitmetriclab.com/api/tools/watts-to-mets.json",
  "formula": {
    "id": "watts_to_mets",
    "expression": "\\text{METs} = \\frac{\\dfrac{11.016 \\times W}{m} + 7}{3.5}",
    "variables": [
      {
        "symbol": "W",
        "description": "Power in watts"
      },
      {
        "symbol": "m",
        "description": "Body mass in kg"
      }
    ]
  },
  "inputs": [
    {
      "id": "watts",
      "label": "Power",
      "type": "number",
      "unit": "W",
      "default": 150,
      "min": 20,
      "max": 500,
      "step": 1
    },
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 30,
      "max": 200,
      "step": 0.1
    }
  ],
  "worked_example": {
    "inputs": {
      "watts": 150,
      "weight_kg": 75
    },
    "expected_output": "8.3 METs"
  },
  "result_summary_template": "A power output of {watts} W for a rider weighing {weight_kg} kg corresponds to approximately {result} under the ACSM leg-ergometry equation.",
  "methodology": "VO₂ (ml/kg/min) = watts × 11.016 ÷ body mass (kg) + 7, the ACSM metabolic equation for leg ergometry (VO₂ = 1.8 × work rate in kg·m/min ÷ mass + 7, with watts converted to kg·m/min at 1 W = 6.12 kg·m/min, so 1.8 × 6.12 = 11.016). METs = VO₂ ÷ 3.5, using the standard resting reference of 3.5 ml/kg/min. Calories per hour = METs × body mass in kg. Derived for steady-state stationary cycling at approximately 50–200 W.",
  "sources": [
    {
      "label": "ACSM's Guidelines for Exercise Testing and Prescription. American College of Sports Medicine.",
      "url": "https://acsm.org/education-resources/books/guidelines-exercise-testing-prescription/"
    },
    {
      "label": "Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990;13(8):555–565.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/2204507/"
    },
    {
      "label": "Compendium of Physical Activities — bicycling MET values. Accessed 2026.",
      "url": "https://pacompendium.com/"
    }
  ],
  "faqs": [
    {
      "question": "Why does body weight change the MET value for the same wattage?",
      "answer": "METs express intensity relative to body mass — millilitres of oxygen per kilogram per minute. The mechanical work of 150 W is fixed, but a 90 kg rider spreads that oxygen demand over more tissue than a 60 kg rider, so the per-kilogram figure is lower. In this equation 150 W is 8.3 METs at 75 kg but 10.6 METs at 55 kg. Absolute calorie burn moves the other way, since the MET energy formula multiplies back by body mass."
    },
    {
      "question": "Can I use this converter for running power from a watch or foot pod?",
      "answer": "The equation is not validated for running. Running power is a modelled estimate rather than a directly braked work rate, and vendors' models disagree with each other by 10–20% at the same pace. The metabolic cost per watt also differs between running and cycling because of elastic energy return in the tendons. For running, pace-based MET tables from the Compendium of Physical Activities are the published route to an intensity estimate."
    },
    {
      "question": "How accurate is the ACSM leg-ergometry equation?",
      "answer": "Validation work places the equation within roughly ±10% of measured oxygen uptake for steady-state cycling between about 50 and 200 W on a stationary ergometer. Accuracy degrades outside that range, during non-steady-state efforts, and for riders whose mechanical efficiency differs from the population average built into the constants. Trained cyclists tend to be slightly more efficient than the equation assumes, so their true VO₂ at a given wattage can sit a little below the estimate."
    },
    {
      "question": "What does the +7 in the equation represent?",
      "answer": "The 7 ml/kg/min constant bundles two costs: resting metabolism (the standard 3.5 ml/kg/min) and the oxygen cost of moving the legs against no external load, which ACSM also sets at 3.5 ml/kg/min for cycling cadences around 50–60 rpm. Together they form the intercept of the equation — the oxygen a rider consumes before the ergometer registers any braked watts. That is why 0 W of external work still corresponds to 2 METs, not 1."
    },
    {
      "question": "Is the MET value from a power meter better than one from a MET table?",
      "answer": "They serve different purposes. A power-derived MET reflects your actual measured work rate in this session, converted through a population-average efficiency. A Compendium table value is a population average for a described activity, with no measurement of your effort at all. When a calibrated power meter is available, the power-derived figure tracks intensity changes far more responsively; the table remains useful when no measurement exists or for non-ergometer activities."
    }
  ],
  "related_tools": [
    {
      "slug": "custom-met-calculator",
      "title": "Custom Activity MET Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/custom-met-calculator.json",
      "page_url": "https://fitmetriclab.com/en/tools/energy-expenditure/custom-met-calculator/"
    },
    {
      "slug": "calories-cycling",
      "title": "Calorie Burn — Cycling",
      "api_url": "https://fitmetriclab.com/api/tools/calories-cycling.json",
      "page_url": "https://fitmetriclab.com/en/tools/energy-expenditure/calories-cycling/"
    },
    {
      "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/"
    }
  ],
  "last_updated": "2026-08-08",
  "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."
}