Water Cooling- 3/8" size?

[DamnFast]

I'm trying to get water hose for my water cooling system.
Everything is 3/8" standard but when I get the hose, is that the inside diameter or the outside diameter?
I am very confused. I am trying to buy the hose from HomeDepot since I don't want to spend more money on hose from online resellers(Their cost is rediculous).

Thanks.

 

[LimeyGreg]

That would be the I.D.

 

[DamnFast]

thanks