Temperature Humidity Index Calculator
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Quick Guide to Use This Calculator
- Step 1: Select the temperature unit (Celsius or Fahrenheit) using the dropdown menu.
- Step 2: Enter the ambient or dry-bulb temperature in the designated input field.
- Step 3: Enter the relative humidity in percentage in the respective input field.
- Step 4: Click the “Calculate THI” button to get the Temperature Humidity Index (THI). THI is a unitless index, so the dropdown sets the unit of the temperature you enter, not the unit of the result.
- Step 5: The result will indicate the stress level for livestock along with the color-coded thermometer.
Color code and ranges are as follows
- Normal, no heat stress (below 68) – Green Color
- Stress Threshold (68 to just under 72) – Yellow Color
- Mild Moderate Stress (72 to just under 80) – Orange Color
- Moderate-Severe Stress (80 to just under 90) – Red Color
- Severe Stress (90 and above) – Purple Color
Formula
With T(db) in Degree Fahrenheit: THI = Tdb – [0.55 – (0.55 x RH/100)] x (Tdb – 58)
With T(db) in Degree Celsius: THI = 0.8 x T(db) + (RH/100) x (T(db) – 14.4) + 46.4
Where T(db) is the ambient or dry-bulb temperature and RH is relative humidity in percent.
Use the temperature unit that belongs to the formula you are reading. The two formulas are not interchangeable: putting a Fahrenheit reading into the Celsius formula inflates the answer by roughly 68 to 90 points and will report severe stress when the real conditions are mild. At 25 Degree Celsius and 50% RH the correct THI is 71.7; feeding 77 Degree Fahrenheit into the Celsius formula returns 139.3, which is not a valid THI at all.
THI is a unitless index, not a temperature, and both formulas report on the same scale. That is why 25 Degree Celsius and its exact Fahrenheit equivalent of 77 Degree Fahrenheit, both at 50% RH, return the same THI of about 71.7. The dropdown above selects the unit of the temperature you enter, not the unit of the answer.
The Fahrenheit form is the index published by the National Research Council (1971); the Celsius form follows Mader, Davis and Brown-Brandl (2006). The stress bands follow Armstrong (1994), with the lower 68 threshold reflecting later dairy research by Zimbelman and Collier.
What is the Temperature Humidity Index (THI)?
The Temperature Humidity Index (THI) is a measure that combines ambient temperature and relative humidity to assess the level of stress and discomfort experienced by individuals, especially animals in a given environment.
Who Can Use This Calculator?
Livestock farmers and caretakers can use this calculator to gauge the comfort levels of animals, ensuring optimal conditions for their well-being.
Industries That Can Use This Calculator
Livestock farming industries can use this calculator. This is useful for dairy farms. Others can also use this calculator to trace their livestock’s behavior.
Benefits of Using This Calculator
- Helps farmers identify potential stress in livestock due to temperature and humidity.
- Allows for timely adjustments in animal management practices to ensure their comfort.
- Aids in preventing heat-related health issues in livestock.
FAQs
How is THI calculated?
THI combines dry-bulb temperature and relative humidity into a single unitless index. This calculator applies the NRC (1971) formula when you enter the temperature in Fahrenheit and the Mader et al. (2006) formula when you enter it in Celsius. Both report on the same scale, where 68 is the stress threshold for dairy cattle and 80 and above is moderate to severe stress.
How does high THI affect livestock?
High THI can lead to heat stress in livestock, impacting feed intake, milk production (in dairy cows), and overall animal well-being.
What measures can be taken to reduce THI for livestock?
Providing shade, proper ventilation, and access to cool water are effective measures to reduce THI for livestock.
Conclusion
The Temperature Humidity Index (THI) Calculator is a valuable tool for livestock farmers to assess and manage environmental conditions for their animals.
By considering temperature and humidity, this tool helps ensure the well-being of livestock and contributes to the overall success of livestock farming operations.