Half inch bigger belt for h/o alt...?

[Denial-]

So this is my first time actually doing things right and getting a high output alternator and doing the big 3 etc. I got a 370 amp alternator from JS alternators and it just got here a few days ago. I opened it up to check it out and read over the instructions with it and on it it's saying I need to put on a half inch shorter belt than the oem one. My main question is how do I know what size belt I need if it's half inch shorter than the original one? I have a 2007 jeep grand cherokee with a 3.7 in it. If anyone could direct me somewhere that would tell me which size belt is oem or mainly what size belt I need for this alternator I'd appreciate it so much.
Also im just wondering why a half inch shorter belt is needed to put this alt in? Does it sit lower than the oem one or what?
Thank you guys for the help. Much love always.

Edit: I did mean shorter* belt in the title but couldn't change it lol

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[metalheadjoe 10+ year member]

Rockauto lists belt length.

 

[spokey9 5,000+ posts]

It has a smaller pulley that's why you need the shorter belt

 

[Popwarhomie 5,000+ posts]

Autozone. Type in car info. Search belt.

Effective Length	86.8in

OEM size # 4060868 (868 would be 86.8")


So you need one 86.3"


Gates K060863
Acdelco 6K863
Napa 6K863
Continental Belt 4060862

 

[some dude]

Hell yeah Pop!

 

[Denial-]

Autozone. Type in car info. Search belt.

Effective Length	86.8in

OEM size # 4060868 (868 would be 86.8")


So you need one 86.3"


Gates K060863
Acdelco 6K863
Napa 6K863
Continental Belt 4060862

Damn.. thank you man... I wasn't expecting you to do all the work for me but I'll definitely take it lol. Thank you so much and also thank you guys for explaining why it needs the smaller belt also. Love you guys for real.