A method of forming an integrated circuit includes placing a first cell layout design of the integrated circuit on a layout design, and manufacturing the integrated circuit based on the layout design. Placing the first cell layout design includes placing a first active region layout pattern adjacent to a first cell boundary, placing a second active region layout pattern adjacent to a second cell boundary, and placing a first set of active region layout patterns between the first and second active region layout patterns, according to a first set of guidelines. The first set of guidelines includes selecting transistors of a first type with a first driving strength and transistors of a second type with a second driving strength. In some embodiments, the first, second and first set of active region layout patterns extend in the first direction, and are on a first layout level.