Different years and models of GMC Sierras have different-sized speakers. It is important to know the correct size of your speakers in case you want to purchase replacements when they go out. Determining your speaker size only takes a few seconds and the simplest of tools. Keep in mind that purchasing an aftermarket stereo system and/or aftermarket speakers can also raise the value of your vehicle. Small upgrades like this can enhance your vehicle's value.
Read the section in your truck's owner's manual dealing with the stereo system. This should provide you with information concerning the speaker size. If you don't have an owner's manual, proceed to the next step.
Open the truck door to access the door panel.
Wipe off the door speaker cover with a shop rag. This will remove any dust and buildup, allowing you to see the outline of the speaker through the venting in the cover.
Examine the outlines of the internal speaker through the speaker cover then stretch a measuring tape across them. All stock Sierra speakers will be either round or oval. The diameter of the speaker, i.e., the widest distance from edge to edge, will determine the size you need to purchase.
