Short answer: every product page has its own size chart, sitting right under the description. Those numbers are the real ones, because a beanie and a hoodie have approximately... nothing in common. :)
Longer answer, plus the questions I actually get:
How do I pick a size?
Go grab a shirt you already own and love the fit of. Lay it flat, measure straight across from armpit to armpit, and compare that number to the Width column on the product page. That's the garment measured flat. The Chest column is your actual body, measured around the fullest part. Two different things, worth knowing which is which before you order.
If you're between sizes: these are unisex cuts, so size up if you want room to move and stay put if you want it closer.
Why no "Men's" or "Women's"?
I use gender-neutral language across the store, so you won't see those here. Instead: Unisex, and eventually Form-Fitting when those pieces drop later this year. It takes a second to get used to.
What if 3XL isn't big enough?
I cap at 3XL right now to keep sizing consistent across product categories. If that leaves you out, reach out and tell me. I'd rather hear about it than have you quietly not order.
Questions, concerns, weird fit situations: just ask!