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WBGT Heat Stress Tool

Wet Bulb Globe Temperature screening for heat risk, outdoor work, athletics, and public safety.

Estimate hourly WBGT using forecast temperature, humidity, wind, and solar radiation inputs. Search a location or use manual values to screen heat stress risk and activity guidance.

Open WBGT Calculator How WBGT Works
Forensic Weather AnalysisExpert Witness SupportStorm Damage ReviewSpecialized ForecastsOutdoor Event ForecastingWBGT MonitoringClimate Risk ReportsFAA Certified UAS PilotAerial Documentation3D Building ImageryFPV 360 FlythroughsConstruction ProgressRoof ClaimsReal Estate Aerial MediaOperational Weather BriefingsTampa Bay Based • Nationwide Remote
Meteorologist-BuiltDesigned around heat-stress communication and weather data interpretation.
Forecast ReadyPulls forecast weather inputs when available using open weather data.
Decision SupportUseful for coaches, job sites, event planners, safety managers, and public officials.
Interactive Tool

Search a location or enter conditions manually.

Calculated values are screening estimates. For official policy, OSHA/NIOSH, athletic association, military, workplace, and local emergency guidance should be followed.

Current Estimate --°F

Search a location or calculate manually.

Low< 80°F
Moderate80–84.9°F
High85–87.9°F
Very High88–89.9°F
Extreme90°F+
TimeTempRHWindSolarWBGTRisk
No forecast loaded yet.
Heat Stress Context

Why WBGT is more useful than temperature alone.

WBGT considers the combined effect of temperature, moisture, wind, and solar loading. It is commonly used to guide heat safety for work, athletics, military training, and outdoor events.

Temperature

Higher air temperatures increase baseline heat stress.

Humidity

Moist air slows sweat evaporation, making cooling less efficient.

Wind

Wind can help evaporative cooling, but hot wind may still be hazardous.

Sun Angle

Direct sunlight and high solar radiation can push risk much higher.

Activity Level

Heavy exertion raises metabolic heat load and lowers safety margins.

Acclimatization

New workers, athletes, and visitors may need stricter rest and hydration plans.

WBGT Calculation Method

How the website’s WBGT estimate is calculated.

The tool uses a screening-style WBGT estimate based on forecast or manually entered air temperature, relative humidity, wind speed, and solar radiation. It is intended for planning and heat-risk awareness, not as a replacement for an official calibrated WBGT instrument.

Step 1

Convert temperature to Celsius.

The input air temperature is converted from Fahrenheit to Celsius so it can be used in the vapor pressure and WBGT equations.

Tc = (Tf − 32) × 5 / 9
Step 2

Estimate saturation vapor pressure.

The tool estimates saturation vapor pressure from air temperature. This describes how much water vapor the air could hold at that temperature.

es = 6.105 × exp((17.27 × Tc) / (237.7 + Tc))
Step 3

Apply relative humidity.

Actual vapor pressure is estimated by multiplying saturation vapor pressure by relative humidity. This is how moisture is brought into the heat-stress estimate.

e = (RH / 100) × es
Step 4

Estimate shaded WBGT.

The base estimate uses a common approximation for shaded WBGT using air temperature and vapor pressure.

WBGTc ≈ 0.567 × Tc + 0.393 × e + 3.94
Step 5

Add a solar loading adjustment.

For outdoor sun exposure, the tool adds a limited solar adjustment based on solar radiation and wind speed. Higher solar radiation increases risk, while stronger wind can reduce the solar adjustment somewhat.

solar adjustment ≈ function(solar radiation, wind speed)
Step 6

Convert back to Fahrenheit and classify risk.

The final value is converted back to Fahrenheit and placed into risk categories such as Low, Moderate, High, Very High, or Extreme. These categories are screening guidance only and should be adapted to policies, activity level, clothing, acclimatization, and local safety rules.

WBGTf = WBGTc × 9 / 5 + 32

Important limitations

This calculator estimates WBGT from available meteorological inputs. True WBGT is ideally measured with a calibrated instrument that directly accounts for natural wet bulb temperature, black globe temperature, dry bulb temperature, radiation, wind, humidity, and local exposure. Use this tool as a planning aid, then defer to OSHA, NIOSH, athletic association, military, employer, emergency management, or local heat-safety guidance when making operational decisions.

WBGT Guidance

Wet Bulb Globe Temperature is a body-stress decision tool.

WBGT accounts for heat, humidity, wind, sun angle, and solar radiation. That makes it more useful than air temperature alone for direct-sun work, athletics, field operations, outdoor events, and heat-safety planning.

< 80°FLower Heat Stress

Generally favorable for most outdoor activity. Hydrate, consider sun exposure, and monitor vulnerable people.

80–85°FElevated

Direct-sun work or exercise can stress the body after about 45 minutes. Plan at least 15 minutes of breaks each hour.

85–88°FHigh

Direct-sun work or exercise can stress the body after about 30 minutes. Take at least 30 minutes of breaks each hour; reduce strenuous activity.

88–90°FVery High

Direct-sun work or exercise can stress the body after about 20 minutes. Take at least 40 minutes of breaks each hour; use shade, cooling, and supervision.

> 90°FExtreme

Direct-sun work or exercise can stress the body after about 15 minutes. Take at least 45 minutes of breaks each hour; postpone or modify strenuous activity when possible.

Medical Relevance

WBGT estimates how hard the body must work to shed heat.

The body cools itself through sweat evaporation and increased blood flow to the skin. High humidity, strong sun, light wind, heavy work, or heat-trapping clothing/PPE can reduce heat loss and raise internal body temperature. That can increase the risk of heat cramps, heat exhaustion, heat injury, and heat stroke.

Heat stress can also reduce fine motor performance, decision-making, productivity, and safety margins — important for construction crews, roofers, athletes, event staff, field teams, drone crews, and outdoor operations.

Changing Climate Context

Heat is becoming an operational planning problem.

As heat and humidity extremes become more frequent, WBGT becomes more valuable for scheduling work/rest cycles, documenting conditions, planning safer outdoor windows, and communicating risk before people become symptomatic.

WBGT focuses on body stress from multiple environmental factors, not simply the forecast high temperature, which is why it is used in occupational, military, athletics, and weather-safety contexts.

Practical Use Cases

Where WBGT adds value.

Outdoor Event Heat Plan

High humidity, full sun, and light wind can require shaded rest stations, hydration reminders, medical staffing, schedule changes, and activity breaks even if the air temperature alone does not look extreme.

Construction / Roofing Operations

Roofing, paving, and construction add metabolic heat, radiant heat, equipment, PPE, and limited shade. WBGT helps determine when to reduce pace, rotate crews, shift work earlier, or increase break frequency.

Athletics and Field Work

WBGT is useful for sports, military, and occupational settings because it gives a more complete view of exertional heat stress in direct sunlight than heat index alone.

Heat Index vs. WBGT

Heat Index tells you how hot it feels. WBGT better estimates outdoor heat stress.

Both tools are useful, but they answer different questions. Heat Index is designed around air temperature and humidity in shaded, light-wind conditions. WBGT adds more of the real outdoor exposure picture by accounting for temperature, humidity, wind, sun angle, and solar radiation.

Heat Index

Best for public “feels-like” heat messaging.

Heat Index combines air temperature and relative humidity to estimate how hot it feels to the human body. It is useful for general public communication, but it does not directly include direct sunlight, changing wind, workload, clothing/PPE, or radiant heat from surfaces.

Use it for: general public heat awareness, forecast messaging, and shaded-condition heat communication.

WBGT

Better for work, sports, events, and direct-sun decisions.

Wet Bulb Globe Temperature is built around heat stress. It better reflects the environmental load on the body because it considers humidity, wind, solar radiation, and radiant heating — the factors that influence how efficiently sweat can evaporate and how fast the body gains or loses heat.

Use it for: outdoor labor, athletics, field operations, drone crews, construction, roofing, event planning, and direct-sun activity decisions.

Why WBGT is often the better operational measurement

WBGT connects the weather to the body’s cooling system.

When the body is under heat stress, it relies heavily on sweat evaporation and blood flow to the skin. High humidity slows evaporation. Strong sun and hot surfaces add radiant heat. Low wind reduces cooling. Heavy work and PPE add internal heat. WBGT captures more of those stressors than Heat Index, which is why it is widely used in occupational, athletic, military, and outdoor safety settings.

In a warmer climate with more frequent high-heat and high-humidity days, WBGT is valuable because it helps organizations move from “it will be hot” to specific decisions: modify schedules, add shade, increase breaks, rotate crews, reduce intensity, monitor symptoms, or postpone activities.

Trusted Heat-Safety Sources

Official and scientific references.

Use these sources for deeper guidance, formal heat programs, and occupational/safety planning.

OSHA Heat ExposureWorker heat illness prevention, water/rest/shade, acclimatization, WBGT, and employer planning. CDC / NIOSH Heat StressOccupational heat stress, metabolic heat, PPE/clothing, illness risk, and prevention resources. NWS WBGT GuidanceWBGT compared to heat index and direct-sun work/rest guidance. NWS Heat SafetyPublic heat-safety tools and weather guidance. Medical Heat Illness OverviewClinical context for heat cramps, heat exhaustion, and heat stroke. Peer-Reviewed WBGT ResearchSearch biomedical literature on WBGT, exertion, worker health, and heat stress.
Important: WBGT guidance is not medical advice and does not replace a formal OSHA/NIOSH heat illness prevention program, athletic trainer guidance, medical direction, or site-specific safety plan. Individual risk varies by acclimatization, workload, hydration, medication, age, medical history, clothing/PPE, shade, and direct sunlight.