Update 11/17: I received size 4 but it's still much too small and I'm inches away from being able to zip the jacket. I think I need to go up another size (to US 6) but I'd rather try it on in store. I'm hesitant to just order another size online.
I had to go up to size 6 in the Barbour Wray vest but this jacket seems to run even smaller.
//// The listing for the other colors mention that this jacket runs small. I ordered 1 size up (US 4).