The purpose of this paper is to suggest a simple way of estimating the thermal load of free form buildings, which can be applied at the early stage of building design. The thermal load of a conventional building is compared with those for the various free form buildings which have the same envelope area. And then, the impact of changes in directional window area ratio and exterior wall area ratio on the thermal load of a free form building are analyzed and expressed as a simple polynomial equation. The thermal load for each case is estimated using TRNSYS 16 with Type 56 of multi-zone building components. The result of this research can be used for designing an energy conservative free form buildings.