5 1/4" I have the same year blazer and i just replaced all my speakers. At least it's 5 1/4" for the door speakers and i can't tell but there's places in the dash board for 4x6" speakers.
6.5S 6.5S
6x9
the speakers in the dash are 4x6s, the speakers in the doors are 6.75in. and the back speakers are 6x9's
16 gal
4x6 in the dash and 6x9 in the rear
36mm
i just recently put new door speakers in a 2000 Chevy blazer. They are 6 and 1/2 in all four doors.
There are 2, 4" x 10" speakers in the celing tward the rear of the full size blazer (next to the hatch glass).
Not sure what size the tweeters are, but the mid range speakers in both the front, and rear doors are 6.5"
The front door panels have 6 1/2" speakers and the rear speakers are 6x9"
235-70-15 or 235-75-15
Dash = 4 in x 6 in Door = 6.5 in Rear = 6 in x 9 in