A method for defining a layout of 3-D devices, such as a finFET, is provided. The method includes determining an area required by a desired 3-D device and designing a circuit using planar devices having an equivalent area. The planar device corresponding to the desired 3-D device is used to layout a circuit design, thereby allowing circuit and layout designers to work at a higher level without the need to specify each individual fin or 3-D structure. Thereafter, the planar design may be converted to a 3-D design by replacing planar active areas with 3-D devices occupying an equivalent area.