This paper considers the need to define comfort of indoor and outdoor spaces in relation to the daily variations of temperature. A graphical tool is presented, which indicates the daily swings of temperature, shown as a single point on a graph representing the average temperature and the maximum temperature swing. This point can be compared with the comfort zones for different activity levels, such as sedentary activity, sleeping, indoor and outdoor circulation according to the design proposals for different spaces. The graph allows the representation of climatic variables, the definition of comfort zones, the selection of bioclimatic design resources and the evaluation of indoor temperatures, measured in actual buildings or obtained from computer simulations. The development of the graph is explained and examples given with special emphasis on the use of thermal mass. (C) 2003 Published by Elsevier Science B.V.