Womens Tank Tops (UK Sizes):

S: 8-10 
M: 10-12 
L: 12-14 
XL: 14-16 

Unisex T-Shirts:
To fit chest size (in inches)

S: 36"
M: 39"
L: 42"
XL: 45"

Unisex Hoodies:
To fit chest size (in inches)

S: 34-36"
M: 36-38"
L: 38-40"
XL: 40-42"