Methods are used to enrich a cell library in such a way to provide a nearly continuous choice of cells to implement a circuit design. The emphasis of the design method is on automatic determination of the needed cell sizes and variants. The method exploits different variants on drive strengths, P/N ratios, topology variants, internal buffering, and so forth. The method allows enriching libraries to become more suitable for efficient timing closure. The method also offers means to adapt the preexisting cells to fit the final distribution, minimizing the number of new cells to be created.