Brake pads arghhhh HELP please :-)

[jack1.8t]

Hi all,
Booked in to Oulton Park on saturday for a track day, and I'm looking to get some performance brake pads to avoid the dreaded brake fade, problem is though, I'm having a lot of difficulty finding out what pads I need!
The car is a B5.5 1.8T Sport estate, 2002 model.
I'm not sure if I've got 288mm or 312mm discs!
I was under the impression that they were 288mm, but when looking online, it gives me the option of 15" wheels, and 16" wheels. Now, my car came with 16" standard alloys, which, online, tells me that I have 312mm discs!
Can anybody shed any light on this matter asap?
Cheers,
Jak