What size of porcelain tiles we should use on small bathroom walls?

[Curiousv]

Have decided to use porcelain. Bathroom walls are 7x8 ..so not big bathroom

What size we should choose on walls. Walls will be green board drywall.

On floor we have deiced to use luxury vinyl planks (not tiles) its concrete floor

 

[Jadnashua]

Some greenboards have a waxy coating on them and are NOT a good idea for use with tile...that wax coating becomes a bond breaker.

As to the size of the tile...use what your significant other likes. Note that the larger the tile, the flatter the surface needs to be. IOW, use straight, unbowed or twisted studs and make sure things are all in the same plane, or you'll have problems getting large tile to set right and look good. If one or more side is greater than 15", the industry standards call for the surface to be flat within 1/8" in 10' and no more than 1/16" in two feet.