Whats the size of the stereo of a 2004 pontiac grand am

The head unit? Or speaker size?

as long as the head unit is not bigger than the original one you can buy an adapter kit that is easy to install at your local parts store

Head unit...I know its a double din but I need to know the size of it so I don't buy one that's too big

if you use crutchfield.com you can put in the year and make of your car and it will give you head units that will fit your vehicle from any number of good quality stereo companies.

Crutch field only gives you the height of the opening not the width. The height is going to be 4”. Most stereo opening widths are 7” wide from 1985 and newer.