Edge trim height for tiles

Hi there,

Will be putting small mosaic tiles around bathtub and plan to put trim to hide edges, the height of the mosaic tile is about 7mm and will be using one of the smallest v shaped notched trowel 5x4mm, just have trouble figuring out the height of the trim, planning on getting 8mm but seems like not much, and 10mm seems like the edge will be higher than the surface, 9mm looks good but not sure it exist in this size, any recommendations wil be appreciated.

Also since I need to get some for front door because also will be doing the floor, I was just trying to figure out what's the rule of thumb, is there a formulae tilers use, such as using the height of tile and the height of the notched trowel to get the trim height.

Thanks in advance.

Cal

I just called BAT, told me for about 1-2 mm more than the tile...