Here is what I have done:
Go to
www.crutchfield.com put in the make and model of your car. Study all of the results as they are usually very accurate. Once you have all of the dimensions and everything, you can check their prices against others. The adapter kits that they sell are in my opinion, worth their weight in gold. Consider this when comparing prices. Crutchfield is out the door with their "free" installation kits which are actually factored into their pricing.