Wet Bulb Calculator / Temperature Formula and Chart

To calculate Wet Bulb Temperature, input Air Temperature, Relative Humidity, and Atmospheric Pressure in calculator. Select your preferred units for temperature (Celsius or Fahrenheit) and pressure (hPa or inHg).

The calculator provides the Wet Bulb Temperature, Dew Point, and Heat Stress Index. This tool is crucial for HVAC Design, Weather Monitoring, and Workplace Safety applications.

Wet Bulb Temperature Chart

Dry Bulb Temperature (°C)	Relative Humidity (%)	Wet Bulb Temperature (°C)
20	90	19.4
20	70	17.6
20	50	15.8
20	30	13.9
25	90	24.5
25	70	22.5
25	50	20.5
25	30	18.5
30	90	29.5
30	70	26.8
30	50	24.2
30	30	21.6

How to Calculate Wet Bulb Temperature?

To calculate Wet Bulb Temperature, combine measurements of Dry-Bulb Temperature, Relative Humidity, and Barometric Pressure. The calculation uses Psychrometric Equations considering the relationship between air temperature, moisture content, and pressure.

The process involves iterative calculations as the wet-bulb temperature is found where the saturation vapor pressure equals the actual vapor pressure at the calculated temperature.

Input:

• Dry-Bulb Temperature (T_d): 30°C
• Relative Humidity (RH): 60%

Calculation: The wet bulb temperature (T_w) can be approximated as follows: T_w ≈ T_d arctan(0.151977 sqrt(RH + 8.313659)) + … ≈ 24.4 °C

Result: 24.4°C

Formula for Wet Bulb Temperature

Basic Stull Formula:

Tw = T × arctan[0.151977(RH% + 8.313659)^(1/2)] + arctan(T + RH%) - arctan(RH% - 1.676331) + 0.00391838(RH%)^(3/2) × arctan(0.023101 × RH%) - 4.686035
where:
Tw = Wet-bulb temperature
T = Air temperature
RH% = Relative humidity percentage

Vapor Pressure Calculation:

es = 6.112 × e^((17.67 × T)/(T + 243.5))
where:
es = Saturation vapor pressure
T = Temperature in Celsius
e = Euler's number (2.71828)

Actual Vapor Pressure:

ea = es × (RH/100)
where:
ea = Actual vapor pressure
es = Saturation vapor pressure
RH = Relative humidity percentage

Example 1: Standard Indoor Conditions

• Air Temperature = 24°C
• Relative Humidity = 50%
• Pressure = 1013.25 hPa
• Wet Bulb Temperature = 17.3°C
• Application = Office HVAC

Example 2: Hot Humid Day

• Air Temperature = 32°C
• Relative Humidity = 80%
• Pressure = 1010 hPa
• Wet Bulb Temperature = 29.4°C
• Application = Heat Stress Monitor

Example 3: Desert Conditions

• Air Temperature = 40°C
• Relative Humidity = 20%
• Pressure = 1000 hPa
• Wet Bulb Temperature = 23.1°C
• Application = Industrial Cooling

Example 4: Cold Winter Day

• Air Temperature = 5°C
• Relative Humidity = 60%
• Pressure = 1020 hPa
• Wet Bulb Temperature = 2.8°C
• Application = Frost Prevention

Example 5: Tropical Climate

• Air Temperature = 28°C
• Relative Humidity = 90%
• Pressure = 1015 hPa
• Wet Bulb Temperature = 26.8°C
• Application = Greenhouse Control

What is Wet-Bulb Temperature?

Wet-Bulb Temperature is the lowest temperature achievable through evaporative cooling of a water-soaked surface. It combines the effects of Air Temperature, Humidity, and Atmospheric Pressure into a single value. This measurement is crucial for understanding human comfort and safety, as high wet-bulb temperatures can indicate dangerous heat stress conditions. Unlike dry-bulb temperature, wet-bulb temperature accounts for the cooling effect of evaporation.