diamond hole cutter size

[zad3717]

Hi, I'm about to tile our bathroom but unsure what size diamond hole cutters I should use.. usual 15mm pipes for sink, toilet is a hidden cistern think its 50mm to the pan.

Any pointers would be appreciated so I have everything I will need.
Thanks

 

[Notch7]

On my shower I used 25mm for a 15mm copper, I figured 5mm all round should be enough