Methods and systems for determining a characteristic of a wafer are provided. One method includes generating output responsive to light from the wafer using an inspection system. The output includes first output corresponding to defects on the wafer and second output that does not correspond to the defects. The method also includes determining the characteristic of the wafer using the second output. One system includes an inspection subsystem configured to illuminate the wafer and to generate output responsive to light from the wafer. The output includes first output corresponding to defects on the wafer and second output that does not correspond to the defects. The system also includes a processor configured to determine the characteristic of the wafer using the second output.