Thanks @neph93
One more thing, and I apologise for being messy in my answers, but I’ve assumed you’re talking about the navy. I don’t know why I did that. The material and cut of the grey is different to the navy. You may want to consider an M in the grey. It is based on the IHT-1610 and they come up a little smaller.
To give you the full picture I take XL in most shirts and like my tees short and fitted. I go for M in the 7.5oz tees and L in the 1610, 6oz bodies. If I wanted a more relaxed fit then it would be L and XL respectively.