A method for determining a best focus and a best dose in the disclosure includes selecting a selection pattern from first and second shot regions of a wafer for split, measuring a critical dimension (CD) value of the selection pattern, thereby deriving a measurement CD value, calculating an effective CD value of the selection pattern for each of the first and second shot regions using the measurement CD value, calculating an upper-limit CD value and a lower-limit CD value of the selection pattern using the effective CD value of the selection pattern, calculating a process window area for the first shot region and a process window area for the second shot region using the upper-limit CD value and the lower-limit CD value of the selection pattern, and comparing the process window area for the first shot region and the process window area for the second shot region with each other.