Measure under the arm and around the fullest part of the chest with arms down, keeping tape horizontal.
Materials and Care
The T-shirt is incredibly fitted. Perhaps it’s my own fault, but I was assuming the shirt to be less fitted and more unisex (the boyfriend shape). I ordered a medium for my 5’4” 150lb self. The shirt fits, but is a lot tighter than I had wanted. Not much room for my boobs.