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Heat Index Calculator

Heat Index Calculator



Air Temperature


Relative Humidity


Dew Point



Table of Content

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The heat index calculator estimates the heat index felt by the human body based on the environmental temperature and relative humidity. The calculator automatically converts the values from one scale to another.

What is the Heat Index?

“The heat index is the temperature or the humidex(humidity index) of temperature felt by the human body”
When you are measuring the heat index, you are taking into account both the temperature and the humidity level of the surrounding environment.

How to Calculate Heat Index?

You can measure the heat index by calculating the environmental temperature, and relative humidity of the surrounding. The heat index may vary significantly in the shaded area and in sunlight due to changes in temperature.
The formula for measuring the Heat Index is:

HI = c₁ + c₂T + c₃φ + c₄Tφ + c₅T² + c₆φ² + c₇T²φ + c₈Tφ² + c₉T²φ²


  •  T = Temperature in °C or °F 
  •  φ = Relative Humidity as a %
  •  c = Constant Parameters dependent on the temperature

The Values of “c” in  °C and °F:

There can be different values of the constant value “c” due to different temperatures. The heat index humidity directly affects the measurement of the heat index. You should consider what is the temp constant “c” for a specific temperature(°C or °F), its values going to change readily for relative temperatures. Try to choose the heat index chart for a specific temperature (°C or °F). You can measure what is the heat index today with the heat index calculator regardless of location. The wet bulb effect would also increase at a higher heat index. 

In the table below the values of “c” in  °C and °F are given:

c₁ -8,785 -42,379
c₂ 1,611 2,049
c₃ 2,339 10,143
c₄ -0,146 -0,225
c₅ -1,231 ⋅ 10⁻² -6,838 ⋅ 10⁻³
c₆ -1,642 ⋅ 10⁻² -5,482 ⋅ 10⁻²
c₇ 2,212 ⋅ 10⁻³ 1,229 ⋅ 10⁻³
c₈ 7,255 ⋅ 10⁻⁴ 8,528 ⋅ 10⁻⁴
c₉ -3,582 ⋅ 10⁻⁶ -1,990 ⋅ 10⁻⁶

Effects of the Heat Index:

The heat index can have potentially severe medical effects on humans. In high heat index conditions, perspiration is hindered due to reduced evaporation as a result of high humidity. The heat index humidity can be difficult to breathe and cramping may happen. Better to use the humidity calculator before traveling to a specific location or destination.
There can be various consequences of the high heat index.

Heat Index Chart:

The following heat index chart describes the precautionary measures at various temperatures.

Celsius Fahrenheit Precautions
27-32°C 80-90°F Fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps.
32-41°C 90-105°F Fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps.
27-32°C 80-90°F Extreme caution: heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke.
41-54°C 105-130°F Danger: heat cramps and heat exhaustion are likely; heat stroke is probable with continued activity.
Over 54°C Over 130°F Extreme danger: heat stroke is imminent.

The heat index calculator indicates the atmospheric conditions of a certain area. The heat index chart may indicate a hot, very hot, warm, and extremely hot heat index.

Despite the rising heat index humidity, the real feels like the temperature calculator may indicate it is bearing heat index

How does Our Calculator Work?

For an accurate estimation of the Heat index, follow the steps:


  • Select the parameter from the list 
  • Enter the relative parameters 
  • Hit the calculate button 


  • Heat index temperature(Celsius, Fahrenheit, Kelvin)  

The dew point, temperature, or relative humidity are interconnected and interconvertible. The heat index calculator will immediately calculate their values.


From the source of Wikipedia: Heat index, Meteorological considerations

From the source of Heat Safety, Heat Disorders