thermally resistive layer

Hi everyone,

I am modeling a pipe with fluid circulating within by coupling heat transfer and fluid flow and the pipe diameter is defined in the geometry section.
i need to define the pipe wall thickness for my pipe as well which i do it with adding a thermally resistive layer in heat transfer physics and define the conductivity as well as the wall thickness.
my question is that considering the pipe wall thickness, is the pipe diameter defined in building the geometry inner diameter or the outer one?

Regards
ASAL