There are two front brake rotor sizes listed at auto parts dealers. There is a 316 mm and a 336mm. Which one will work on my 2004 XC90 T6?

 

FCP has a blog post and a measuring template on their web site to determine your size. Different models used different sizes depending on trim packages and serial number so you may also just want to call them (or IPD USA if you are on the west coast and give them your VIN.

This has been discussed on other threads as well with tricks like looking at the stamping on the edge of the rotor so check out the thread search tool as well.