Find a shirt/Jacket that fits you perfectly, lay it down on the floor or on a flat surface, measure straight across the chest from seem to seem directly under the armpits, then multiply that number by 2. This will be your chest width, if the size you measure is in between sizes then always order the bigger size. For example, if you are 46″ Chest then choose XL instead of L in our Unisex shirts. Please note that our Ultra Lightweight Performance Fabric can feel smaller compared to regular polo shirts and jackets. While the inch sizes shown are exact measurements, these are subject to production tolerances.