Calculate wet-bulb temperature from dry-bulb and relative humidity. Includes dew point, heat index, WBGT, heat stress risk assessment, and RH lookup table.
The **Wet-Bulb Temperature Calculator** determines the wet-bulb temperature from dry-bulb temperature and relative humidity. Wet-bulb temperature — the lowest temperature achievable through evaporative cooling — is a critical metric for heat safety, HVAC design, cooling tower performance, and climate science.
When wet-bulb temperature exceeds 35°C (95°F), the human body can no longer cool itself through sweating, making outdoor activity lethal regardless of fitness level. Even wet-bulb temperatures of 28-32°C pose serious risks for strenuous activity. This calculator uses the Stull (2011) formula, accurate to ± 0.3°C for typical meteorological conditions.
The tool provides wet-bulb temperature, dew point, wet-bulb depression, heat index, simplified WBGT, a heat stress risk assessment with color-coded danger levels, a visual temperature scale, and a comprehensive RH lookup table. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case. Use the example pattern when troubleshooting unexpected results.
Wet-bulb temperature is the most important metric for heat safety and evaporative cooling design. It determines cooling tower performance, workplace heat exposure limits, and climate habitability. Keep these notes focused on your current workflow. Tie the context to real calculations your team runs. Use this clarification to avoid ambiguous interpretation. Align the note with how outputs are reviewed.
Tw ≈ T × atan(0.151977 × √(RH + 8.313659)) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838 × RH^1.5 × atan(0.023101 × RH) − 4.686035 (Stull 2011 formula, where T in °C, RH in %) Relationship: Dew Point ≤ Wet-Bulb ≤ Dry-Bulb (always)
Result: Tw = 28.1°C (High risk)
At 35°C dry-bulb and 60% RH, the wet-bulb temperature is 28.1°C — in the "High risk" zone for heat stress. Wet-bulb depression is 6.9°C, indicating moderate evaporative cooling potential. The dew point is 26.2°C. This combination would make outdoor labor dangerous without frequent rest and hydration.
The wet-bulb temperature is increasingly recognized as the key metric for heat mortality risk. Traditional heat indices combine temperature and humidity but can be misleading. A dry 50°C day (Tw ≈ 25°C) is survivable with shade and water, while a humid 38°C day (Tw ≈ 34°C) at the same heat index is far more dangerous because evaporative cooling fails.
Research by Sherwood and Huber (2010) established Tw = 35°C as the theoretical human survivability limit. More recent studies (Vecellio et al., 2022) found that in practice, young healthy adults begin struggling at Tw = 31°C under moderate activity. Elderly and chronically ill individuals face danger at even lower thresholds.
**HVAC Design:** Building cooling systems are sized based on outdoor wet-bulb design conditions. ASHRAE provides 0.4%, 1%, and 2% design wet-bulb temperatures for locations worldwide. In Houston: 0.4% Tw = 26.7°C. In Phoenix: 0.4% Tw = 21.1°C — explaining why evaporative cooling works in Phoenix but not Houston.
**Data Center Cooling:** Large data centers emit massive amounts of heat. Free cooling (using outdoor air or evaporative methods) is possible when the outdoor wet-bulb temperature is below the supply air temperature — typically below 18-22°C. Locations with low Tw (like Oregon or Iceland) save millions in cooling costs compared to humid locations.
Global warming increases wet-bulb temperature through two mechanisms: higher air temperature and increased evaporation (more moisture in the atmosphere). The Persian Gulf, South Asian subcontinent, and equatorial regions are most vulnerable. By mid-century, wet-bulb temperatures exceeding 32°C may occur for weeks at a time in heavily populated areas, threatening billions of people who lack air conditioning.
It is the temperature a thermometer reads when wrapped in a wet cloth with air flowing past it. Evaporation cools the thermometer: the drier the air, the more cooling, and the lower the wet-bulb temperature. At 100% RH, wet-bulb equals dry-bulb (no evaporation possible).
Humans cool by sweating: sweat evaporates, removing heat. When Tw = 35°C (body core temperature), evaporation stops because the air can hold no more moisture at body temperature. Without cooling, core temperature rises uncontrollably, leading to heat stroke and death within hours.
Wet-Bulb Globe Temperature combines wet-bulb (70%), black-globe radiation (20%), and dry-bulb (10%). OSHA and military use WBGT to set work-rest cycles: <25.6°C = unrestricted, 25.6-27.8°C = limited heavy work, >32.2°C = minimal activity. This calculator provides a simplified outdoor estimate.
Cooling towers cool water to within 3-8°C of the wet-bulb temperature (this difference is called "approach"). A location with Tw = 25°C can cool tower water to ~28-33°C. Lower wet-bulb = better cooling performance. Cooling tower design is based on the 1% design wet-bulb temperature.
Yes. Several locations have already briefly reached Tw > 35°C: Jacobabad (Pakistan), Ras al Khaimah (UAE). Climate projections show that by 2100, large populated regions in South Asia, the Persian Gulf, and the US Gulf Coast could regularly exceed Tw = 32-35°C during heat waves.
Both involve moisture, but dew point is the temperature at which condensation begins (cooling air at constant moisture). Wet-bulb is the temperature of evaporative cooling (adding moisture to air). Relationship: dew point ≤ wet-bulb ≤ dry-bulb, always.