Wet Bulb Calculator
Calculate wet bulb temperature and heat stress risk from temperature and humidity
Calculate Wet Bulb Temperature
Air temperature measured by standard thermometer
Percentage of water vapor in air
Wet Bulb Depression
Relative Humidity
Formula Used
Stull Formula (Wet Bulb):
Tw = T × arctan[0.151977 × √(RH + 8.313659)] + arctan(T + RH) - arctan(RH - 1.676331) + 0.00391838 × RH^(1.5) × arctan(0.023101 × RH) - 4.686035
Where: T = dry bulb temp (°C), RH = relative humidity (%), Tw = wet bulb temp (°C)
Example Calculation
Summer Heat Wave Scenario
Dry Bulb Temperature: 35°C (95°F)
Relative Humidity: 70%
Location: Outdoor work environment
Concern: Worker safety during heat wave
Stull Formula Calculation
1. Apply Stull formula with T = 35°C and RH = 70%
2. Calculate: Tw = 35 × arctan[0.151977 × √(70 + 8.313659)] + ...
3. Result: Wet bulb temperature ≈ 31.1°C
4. Assessment: Very high heat stress - physical labor becomes difficult
5. Wet bulb depression: 35°C - 31.1°C = 3.9°C
Recommendation: Frequent breaks, hydration, and heat stress monitoring essential
Heat Stress Levels
<16°C (61°F)
Low - Comfortable
16-22°C (61-72°F)
Moderate - Caution
22-28°C (72-82°F)
High - Limit activity
28-32°C (82-90°F)
Very High - Difficult labor
>32°C (90°F)
Extreme - Dangerous
WBGT Risk Levels
<18°C
Minimal risk
18-23°C
Low risk
23-28°C
Moderate risk
28-32°C
High risk
>32°C
Extreme risk
Key Concepts
Wet Bulb: Lowest temperature achievable by evaporative cooling
Humidity Effect: Higher humidity reduces cooling efficiency
WBGT: Includes solar radiation and wind effects
Heat Stress: Body's ability to regulate temperature
Understanding Wet Bulb Temperature
What is Wet Bulb Temperature?
Wet bulb temperature is the lowest temperature that can be reached through evaporative cooling only. It's measured using a thermometer wrapped in water-soaked fabric and ventilated, simulating the cooling effect of sweat evaporation from human skin.
Why It Matters for Health
- •Body Cooling: Represents human body's cooling limit through sweating
- •Heat Stress: Above 35°C (95°F) becomes dangerous for extended exposure
- •Humidity Impact: High humidity reduces cooling efficiency significantly
Applications
Wet bulb temperature is critical for various fields including meteorology, occupational safety, construction planning, and climate assessment.
Key Applications
- •Occupational Safety: Work safety guidelines and heat illness prevention
- •Sports Medicine: Athletic performance and safety in hot conditions
- •Construction: Building material selection and worker safety
- •Meteorology: Weather forecasting and climate analysis
Calculation Methods and Formulas
Stull Formula (accurate 5-99% RH)
Complex empirical formula for wet bulb
WBGT = 0.7×Tw + 0.3×T (indoor)
Wet Bulb Globe Temperature
WBGT = 0.7×Tw + 0.2×Tg + 0.1×T
Outdoor WBGT with solar radiation
Depression = T - Tw
Wet bulb depression (cooling potential)
• Accurate for -20°C to +50°C
• Valid for 5-99% relative humidity
• Error range: -1°C to +0.65°C
• Evaporative cooling simulation
• Humidity limits cooling rate
• Body heat regulation model
• 35°C wet bulb = human limit
• WBGT guidelines for workers
• Climate change implications