{
  "slug": "wbgt-heat-stress",
  "title": "WBGT Heat Stress Calculator",
  "heading": "WBGT Heat Stress & Activity Guidance Calculator",
  "category": "fitness-health",
  "url": "https://www.revenuelab.fyi/toolbox/wbgt-heat-stress",
  "summary": "Estimate Wet Bulb Globe Temperature and safe work/exercise guidance in the sun.",
  "description": "Wet Bulb Globe Temperature (WBGT) is the standard heat stress index used by the military, OSHA, and high school athletic associations because unlike heat index, it accounts for direct solar radiation and wind in addition to humidity and air temperature. This calculator uses a simplified approximation that estimates WBGT from air temperature, relative humidity, and whether you're in direct sun or shade, mapping the result onto standard flag-based activity guidance (green/yellow/orange/red/black) used in sports heat acclimatization protocols. A true WBGT reading requires a specialized meter with a black globe thermometer, so treat this as a planning estimate, not a substitute for an on-site instrument when heat stress liability is on the line.",
  "formula": "WBGT ≈ 0.7×Tw + 0.2×Tg + 0.1×Td, approximated here from T and RH using a natural wet bulb estimate and a sun-exposure globe temperature adjustment.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=wbgt-heat-stress",
  "inputs": [
    {
      "id": "temp",
      "label": "Air temperature",
      "kind": "number",
      "hint": null,
      "default": 92,
      "unit": "°F",
      "min": 60,
      "max": 120
    },
    {
      "id": "rh",
      "label": "Relative humidity",
      "kind": "number",
      "hint": null,
      "default": 55,
      "unit": "%",
      "min": 5,
      "max": 100
    },
    {
      "id": "sun",
      "label": "Sun exposure",
      "kind": "select",
      "hint": null,
      "default": "full",
      "options": [
        {
          "value": "full",
          "label": "Full direct sun"
        },
        {
          "value": "partial",
          "label": "Partial shade"
        },
        {
          "value": "shade",
          "label": "Full shade"
        }
      ]
    }
  ],
  "outputs": [
    {
      "id": "wbgtF",
      "label": "Estimated WBGT",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "wbgtC",
      "label": "WBGT (°C)",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "flag",
      "label": "Activity flag guidance",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Air temperature: 92 °F",
      "Relative humidity: 55 %",
      "Sun exposure: Full direct sun"
    ],
    "outputs": [
      "Estimated WBGT: 84.5",
      "WBGT (°C): 29.2",
      "Activity flag guidance: Yellow — moderate risk"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter air temperature (°F).",
      "Enter relative humidity (%).",
      "Enter sun exposure.",
      "Read your estimated wbgt 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": {
        "temp": 60,
        "rh": 33,
        "sun": "full"
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "temp": 92,
        "rh": 55,
        "sun": "full"
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "temp": 120,
        "rh": 88,
        "sun": "full"
      }
    }
  ],
  "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 is WBGT different from heat index?",
      "a": "Heat index assumes shade and light wind and is calibrated for general public reporting. WBGT adds direct solar radiation via a black globe thermometer reading and is designed specifically for people exercising or working outdoors in the sun, which is why it's the standard for sports and military heat safety protocols instead of heat index."
    },
    {
      "q": "What do the flag colors mean for practice or work?",
      "a": "Most high school athletic association guidelines start mandatory water breaks and reduced equipment at yellow, require significant activity modification at orange, limit practice to light activity with frequent breaks at red, and cancel outdoor activity entirely at black flag conditions."
    },
    {
      "q": "Can I get a truly accurate WBGT without a meter?",
      "a": "Not precisely — this calculator is a documented approximation (Stull's formula for natural wet bulb temperature plus an estimated globe temperature boost for sun exposure), useful for planning, but organizations with heat safety liability should use an actual WBGT meter with a real black globe sensor on site."
    },
    {
      "q": "Why does wind speed matter for real WBGT but isn't in this simplified version?",
      "a": "Wind affects both the natural wet bulb and black globe readings in a true WBGT meter — more wind cools the globe and speeds evaporation. This simplified estimate omits wind for usability, so treat results as slightly conservative (underestimating cooling) in windy conditions."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/heat-index-calculator",
    "https://www.revenuelab.fyi/toolbox/uv-exposure-burn-time"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — WBGT Heat Stress Calculator (https://www.revenuelab.fyi/toolbox/wbgt-heat-stress)"
}