Thanks, I found this from Jezzie:
Female Shirts -
Get AT LEAST one size larger than normal!!!!!!!!!!!!! Female Physical Conditioning shirts (fitted t-shirts) are VERY tight! Neck hole, arm holes, shoulders, everything.
Normally i wear a size small in normal average t-shirts, I got medium PC shirts and they're sooo tight! next time i get some i'm getting large and they'll still fit tighter than normal tshirts!!