Sorry to revive such an old thread but I just completed this serpentine belt replacement (which was super easy) and all the info I found on the internet didn't help me with the proper size.
My truck is a 1999 Mazda B3000 3.0 V6, 2wd, power steering but no A/C.
I solved my chirping/squeaking belt by replacing the dayco belt with a gatorback belt which is now called a:
Continental Elite Poly-V Belt w "quiet Channel" technology
All the local parts source stores said I needed a 85.5" belt, which was incorrect. What I needed was an 86" belt, part no# 4060860.
Hope it helps someone out.