Hey everyone im new here and cant seem to find what im looking for.

I have a 2007 Tahoe LS and there 2 spots for speakers in the rear of my truck. Right by the rear hatch door, one spot on here side of the rear glass.

Anyways my truck didnt come with them and i want to put some in to help the sound. What size are they? i know they cant be big im thinking 3" maybe