The easiest way to nail your size is to measure your chest. Grab a soft tape measure, wrap it around the fullest part of your chest, and keep it level under your arms. Don't suck in, don't puff out—just stand naturally. Write that number down.

Then, check Windbar's size chart. It's usually listed on the product page. Match your chest measurement to the closest size. If you're between sizes, go with the larger one if you want a true boxy fit, or the smaller one if you want it to sit a bit closer to the body.

Don't rely on your old tees' size labels. Brands cut differently, and even within the same brand, a boxy tee will fit differently than a slim one. Trust the numbers.