ladybug_comfort.hi module

Utility functions for calculating Heat Index (HI).

ladybug_comfort.hi.heat_index(ta, rh)[source]

Calculate heat index (HI) from air temperature and relative humidity.

Heat index is derived from original work carried out by Robert G. Steadman [1], which defined heat index through large tables of empirical data. The formula here approximates the heat index to within +/- 0.7C and is the result of a multivariate fit [2]. Heat index was adopted by the US’s National Weather Service (NWS) in 1979.


[1] Steadman, R. G. (July 1979). “The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science”. Journal of Applied Meteorology. 18 (7): 861–873.

[2] Lans P. Rothfusz. “The Heat Index ‘Equation’ (or, More Than You Ever Wanted to Know About Heat Index)”, Scientific Services Division (NWS Southern Region Headquarters), 1 July 1990.

  • ta – Air temperature [C]

  • rh – Relative humidity [%]


hi – Heat index [C]


Get the category of warning associated with a given heat index (HI).

Categories are used by the US National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) to issue the following warnings:

  • 0 = No Warning. Satisfactory temperature. Can continue with activity.

  • 1 = Caution: Fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps.

  • 2 = Extreme caution: Heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke.

  • 3 = Danger: Heat cramps and heat exhaustion are likely. Heat stroke is probable with continued activity.

  • 4 = Extreme danger: Heat stroke is imminent.


hi – Heat index [C]


category – An integer indicating the level of warning associated with the heat index. Values are one of the following:

  • 0 = No Warning

  • 1 = Caution

  • 2 = Extreme Caution

  • 3 = Danger

  • 4 = Extreme Danger