They run similar to stores like Gap and J. Crew. You'd probably take a small at Express if you are a 2/4 at ON.

I find that their tops are very long for me (5' 2"). Can any of the others confirm?

I wear the same size as you and find Express to run pretty TTS. Their jeans fit me poorly though. 2 is too small and 4 is too big.

Elpgal, I don't have a problem with their tops (I like them on the long side anyway), but I find their skirts are always too long and they often have details like ruffles or trims that makes them difficult to hem.

I have found everything at Express to be incredibly long on me which is why I haven't shopped there in years.