* Your vehicle's paperwork: The original window sticker or owner's manual will specify the size.
* The rim itself: The size is stamped on the inside or outside of the wheel. Look for something like "16x7" (diameter x width).
* Your tire sidewall: The tire size (e.g., P215/65R16) will indicate the rim size (16 in this example).
Without more information about your specific 2003 Impala, I cannot give you a definitive answer.
