Congratulations on the store launch!
While contemplating what size to get, I saw that you can buy Kagi T-shirts from XS to XL, but the size chart ( https://store.kagi.com/pages/size-chart ) only covers S to XL.
Also, the specified width measurements are weirdly large. I'm 195cm tall and I'm usually wearing size L T-Shirts, but if I measure my existing T-Shirts - even the baggy ones - while the height roughly corresponds, all my size L T-Shirt widths are smaller than your S size? Are these T-Shirts really that baggy? How tall are your models in the photos and what size are they wearing?
The size chart should also contain the measurements for XS.
