We can't state this enough:

All our garments are designed and cut to do a specific job >> RUN.

Which is why they will run on the smaller size than what you're likely used to. They are technical garments that hug the torso more, because lots of loose fabric flapping about as you run isn't a good thing. 

If in doubt please refer to size/measurement charts found with each specific product.

But...

In general we do advise to size-up one -- unless you're really after that extra fast AF race day fit.