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Wet Bulb Calculator

Enter temperature, relative humidity, and optional global temperature to find wet bulb temperature and wet bulb globe temperature (indoor/outdoor).

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Wet Bulb Calculator

Access this wet bulb calculator to determine the wet bulb and wet bulb globe temperature (WBGT) for indoor and outdoor environments. It is an Ideal tool that helps to assess heat stress, optimize HVAC systems, and ensure worker safety by calculating WBGT temperature.

What Is Wet Bulb Temperature?

This meteorological parameter is widely used to measure the cooling effect of evaporation on the human body. Wet bulb temperature merges the effect of temperature and humidity in one single value.

Key-Points:

  • Wet bulb temperature is mostly lower than the dry bulb temperature(normal air temperature) 
  • When the humidity is at its maximum value (100%) in the air, then the wet bulb temperature is equal to the dry bulb temperature
  • As the humidity becomes lower, the wet bulb temperature goes lower than the normal temperature

How Is It Measured?

Using A Psychrometer:

This is a specific tool that is designed to calculate the humidity. It contains two thermometers:

  • Use the bulb thermometer to measure the air temperature
  • Note down the reading of the wet bulb thermometer
  • Compare the readings of both thermometers to get the wet bulb temperature 

DIY Method:

  • Take a cloth and thermometer
  • Soak the cloth in water, and wrap it up on the bulb of the thermometer to measure the wet bulb temperature

Why Is It Important?

Wet bulb temperature helps to determine the body's ability to cool itself through sweating. When you are in a more humid environment, then the water evaporates more slowly. Therefore, the body can't cool down easily. In this kind of environment, humans need to calculate the wet bulb temperature. The high wet bulb temperature indicates a greater risk of low cooling efficiency and getting ill (heatstroke, hyperthermia).

In industries like construction, agriculture, and sports, wet bulb temperature helps to provide the right working environment to the workers who are exposed to outdoor and indoor high-temperature areas. 

Wet Bulb Temperature Chart:

Wet Bulb Globe Temperature From WBGT and Relative Humidity%
Humidity% Temperature in Degrees Farenheit
0 59.0 60.8 63.4 60.8 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8 107.6 109.4
10 59.0 60.8 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8 107.6
20 60.8 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8 107.6
30 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8
35 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2
40 66.2 68.0 69.8 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 91.4 93.0 95.0 96.8 98.6 102.2
45 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 89.6 91.4 95.0 96.8 98.6 98.6 102.2
50 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 95.0 96.8 98.6 102.2
55 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 95.0 96.8 98.6 100.4
60 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 86.0 87.8 89.6 91.4 95.0 96.8 98.6 100.4
65 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 87.8 89.6 91.4 95.0 96.8 98.6 100.4
70 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 91.4 96.8 100.4 102.2

 

What Is The Wet Bulb Globe Temperature?

The wet bulb globe temperature(WBGT) is a measure of the heat stress in direct sunlight, which affects humans. WBGT measures heat by considering all the four major environmental heat factors:

  • Air Temperature 
  • Humidity
  • Radiant Heat (heat coming from sunlight or sources such as furnaces) 
  • Air Movement (wind or ventilation)

How To Calculate Wet Bulb Temperature?

To calculate wet bulb temperature, determine:

  • Dry Bulb Temperature (T): The standard air temperature
  • Relative Humidity (RH): The percentage of moisture in the air

\(\ T_w = T * arctan[0.152 * (rh + 8.3136)^{1/2}] + arctan(T + rh\%) – arctan(rh – 1.6763) + 0.00391838 *(rh)^{3/2} * arctan(0.0231 * rh) – 4.686\)

Where:

  • Tw = Wet Bulb Temperature
  • T = Dry Bulb Temperature
  • rh = Relative Humidity

In order to determine the wet bulb globe temperature (WBGT), you have to measure:

  • Globe Temperature (Tg): Use a black globe thermometer to measure it

WBGT Formula:

For outdoor conditions (with direct solar radiation):

WBGT = 0.7Tw + 0.2Tg + 0.1T

For indoor conditions:

WBGT = 0.7Tw + 0.3T

Example: 

Calculate wet bulb temperature, also find outdoor and indoor WBGT index for the following values:

  • Dry Bulb Temperature (DBT) = 40°C
  • Relative Humidity = 80%
  • Globe Temperature (GT) = 35°C

Solution:

\( \text{Calculate}\ 0.151977 \cdot (\text{rh}) + (8.313659)^{1/2}: \)

\(\ =\ 0.151977 \cdot (80 + 8.313659)^{1/2} \approx 0.151977 \cdot (88.313659)^{1/2} \approx 0.151977 \cdot 9.399 \approx 1.428 \)

\(\text{Find arctan(1.428):}\)

\(\text{= arctan(1.428) ≈ 0.963 radians}\)

\(\text{Calculate arctan(T + rh):}\)

\(\text{= arctan(40 + 80) = arctan(120) ≈ 1.563 radians}\)

\(\text{Calculate (arctan(rh} - 1.676331):\)

\(\text{ = arctan(80 - 1.676331) = arctan(78.323669) ≈ 1.558 radians}\)

\(\text{Solve}\ 0.00391838 \cdot \ (rh)^{3/2} \cdot \arctan(0.023101 \cdot \ (rh): \)

\(\ =\ (rh)^{3/2} = 80^{3/2} = 80^{1.5} \approx 715.5 \)

\(\text{ = 0.023101 * 80 = 1.848  arctan(1.848) ≈ 1.072 radians}\)

\(\ = 0.00391838 * 715.5 * 1.072 ≈ 3.010\)

\(\text{Now, combine all the calculated parts in the formula:}\)

\(\ T_w = 40 \cdot 0.963 + 1.563 - 1.558 + 3.010 - 4.686 \)

\(\text{Calculate the final result:}\)

\(\ T_w = 38.52 + 1.563 - 1.558 + 3.010 - 4.686 \)

\(\text{Natural Wet Bulb Temperature (NWB)} ≈ 36.85°C\) 

The wet-bulb temperature is approximately 36.85°C, which is high and poses a significant risk of heatstroke.Therefore, it is necessary to take immediate action such as seeking shelter in an air-conditioned environment, staying hydrated, and minimising physical activity to protect yourself. Still, if there are symptoms of heatstroke, get medical attention instantly!

\(\text{Now, for calculating outdoor WBGT, add values in the given formula:}\)

\(\text{WBGT(Outdoor) = 0.7 * 36.85 + 0.2 * 35 + 0.1 * 40}\)

\(\text{WBGT(Outdoor) = 25.795 + 7 + 4}\)

\(\text{WBGT(Outdoor) = 36.795°C}\)

\(\text{Put values in the wet bulb globe temperature (Indoor) formula:}\)

\(\text{WBGT(Indoor) = 0.7(36.85) + 0.3(40)}\)

\(\text{WBGT(Indoor) = 25.795 + 12 = 37.795°C}\)

WBGT is a valuable metric for safeguarding human health in hot and humid environments. So, the best practice is to find the WBGT and it can be easily figured out with a wet bulb temperature calculator.

Note: A wet bulb temperature higher than 35°C(95 °F), can be dangerous for humans.

Why Is WBGT (Wet Bulb Globe Temperature) Essential To Measure?

It helps to understand the environmental heat conditions. This combination of high heat and humidity is potentially harmful to humans. Therefore, it is essential to determine the WBGT temperature and measure it.

This information is necessary for:

  • Preventing heat-related illnesses
  • Enhancing workplace safety
  • Protecting vulnerable populations
  • Optimizing athletic performance

FAQ’s:

Is A Wet-Bulb The Same As A Dew Point?

The wet bulb temperature and dew point parameters are both related to the moisture content in air but they measure different aspects. The wet bulb measures the air's capacity to cool through evaporation while the dew point indicates the quantity of moisture content in the air.

Why Is A Wet-Bulb Important In HVAC?

It has great importance in HVAC systems because it is related to the capacity of the air to absorb moisture. This relationship significantly impacts HVAC system design, operation, and performance.

Here are the key roles of wet bulb temperature in HVAC:

  • Evaporative Cooling
  • Dehumidification 
  • System Performance 
  • Energy Efficiency

Therefore, measuring the wet bulb temperature is crucial for HVAC professionals, which can be readily calculated using our wet bulb calculator. It automates the measurement process and delivers the data needed to optimize HVAC systems. 

How Long Can You Survive Wet-Bulb Temperature?

Exposure to extremely high wet bulb temperatures is life-threatening. There is no exact limit for survival. Factors such as individual health, physical exertion, access to cooling, and acclimatization can influence the time it takes for heat-related illness to occur.

How To Survive A Wet Bulb Event?

In extremely high temperatures, using an air conditioner is necessary for survival. When the wet bulb temperature reaches an extreme temperature threshold (e.g., above 35°C), then it poses a great threat to human life. 

Here’s what you need to do:

  • Seek Immediate Shelter: Immediately move towards a shelter, basement, or air-conditioned place
  • Stay Hydrated: Drink an adequate amount of water, juices, and squash throughout the day (at least 64 ounces but adjust your intake based on your body's needs)
  • Minimize Physical Activity: Reduce your work, take frequent breaks, and do some rest under the shaded area 
  • Cool Down the Body: Take a shower, and apply cold compresses to the wrists and neck. Wear loose and light-colored clothes
  • Monitor Vulnerable Individuals: Keep an eye on children, elder persons, and those who have underlying health conditions
  • Call For Help: If you are experiencing the symptoms of heat like high heartbeat, dizziness, etc, call for help or contact emergency services

References:

From the source of Wikipedia: Wet-bulb temperature.