The purpose of this paper is to suggest a simple way of determining the thermal characteristic of free-form buildings, which can be applied at an early stage of the design phase. The thermal load of a reference building estimated using TRNSYS 16 is compared with those for various free-form buildings that have the same envelope area as the reference building. A database of thermal load ratios (i.e. the ratio of the free-form building's thermal load over the reference building's thermal load) was generated. Then, polynomial equations returning the envelope heat gain, heat loss, and solar heat gain ratios were derived as a function of window area ratio and exterior wall area ratio of a free-form building. It was found that the proposed models are able to predict the heat gain, heat loss, and solar heat gain characteristics of a free-form building within 10% of discrepancy, compared with detailed thermal load simulation results. (C) 2012 Elsevier Ltd. All rights reserved.