Tough to call as they look almost identical. The 17's have a little notch in the side of the center cap so it pops off easy. The 18's which I have are notch-less. Clean wheels none the less as not many MKV's have them. I would say they are 18's. Good OEM wheel thread here.

The OEM Wheel Thread - VW GTI Forum / VW Rabbit Forum / VW R32 Forum / VW Golf Forum - Golfmkv.com