The WBGT heat stress index has been well tested under a variety of climatic conditions and quantitative links have been established between WBGT and the work-rest cycles needed to prevent heat stress effects at the workplace. While there are more specific methods based on indi-vidual physiological measurements to determine heat strain in an individual worker, the WBGT index is used in international and national standards to specify workplace heat stress risks. In order to assess time trends of occupational heat exposure at population level, weather station records or climate modelling are the most widely available data sources. The prescribed method to measure WBGT requires special equipment which is not used at weather stations. We compared published methods to calculate outdoor and indoor WBGT from standard climate data, such as air tempera-ture, dew point temperature, wind speed and solar radiation. Specific criteria for recommending
a method were developed and original measurements were used to evaluate the different methods. We recommend the method of Liljegren et al. (2008) for calculating outdoor WBGT and the method by Bernard et al. (1999) for indoor WBGT when estimating climate change impacts on occupational heat stress at a population level.