How do I change speaker size in my car?

How do I measure the EXACT size of a car speaker?

• When I'm replacing bad speakers and ordering new ones off the web, how can I make sure that the mount holes on the replacement speakers are the same exact spacing as the mount screws on my car? If (just as a nice round number - not the actual size that I need) replacement speakers are advertised as "5 inches", does that mean that the CENTERS of the MOUNT HOLES are 5 inches apart DIAGONALLY...or does it mean that the CENTERS of the MOUNT HOLES are 5 inches apart ADJACENT...or does it mean something else? Obviously if the mount holes configuration of replacement speakers is not the same and the original speakers, it is INFINITELY more trouble to replace car speakers. For what it's worth, I'm looking for round replacement speakers (low cost - for a 15-year-old car) that have mount holes that are right at 4-3/4 inch apart from each other DIAGONALLY... (and 4 OHM)

• Answer:

  Add info what car it is excactly.