Hello,
Thanks for you email and inquiry on our sizing.
Generally I'd recommend sticking with your usual size, the large.
But I'd like to give you the garment dimensions for our Men's Capilene 3 Zip Neck Shirt.
I'd suggest taking these to a shirt that you have and see how this compares.
In the medium the chest circumference is 42.5", the front lengthis 25.75" (collar seam to the hem) and the sleeve length is 32.25" (from the highpoint of the neckline to the wrist).
In the large, the chest is 46.5", the front length is 26.75" andthe sleeve is 33.25"
I hope that helps and let us know if you have any other questions.