16 1/2” underarm to underarm In excellent condition! Details from the website: Men's P.R.O. Mesh Jersey combines class leading aerodynamic design with highly breathable mesh to make the ultimate high-performance summer jersey. Features: - PRO Transfer In-R-Cool mesh main body for maximum breathability and quick drying - PRO Aero fabric in key leading-edge areas reduces aerodynamic drag - Patented anatomic Speed Sleeve construction optimizes fit in the cycling position - Longer to-the-elbow sleeves reduce drag around upper arms - Compressive feel for on-the-bike performance - Clean raw-edge mesh arm openings for seamless transition to skin - Low neckline for hot weather comfort - Full-length semi-auto lock zipper can be flipped up and pulled open with one hand for easy venting