This study develops a novel approach to predict the outdoor temperature fluctuations during daytime as a dimensionless temperature variation coefficient. In this approach, the daily outdoor temperature trend is established by using the daily maximum and minimum temperatures. A case study is performed to calculate the cooling degree-hours for 58 cities in different geographical regions of Turkey as a case study for the present approach. The results are then compared with the published data. The other advantage of this approach is that it allows the prediction of monthly cooling degree-hours for buildings. (C) 2011 Elsevier Ltd. All rights reserved.