From the brand: Non-wire bra sizing can vary by preference and desired coverage, particularly in this collection where the back closure is more adjustable than traditional bras. If you prefer more coverage, they suggest sizing up and adjusting the band to be smaller.

PATINA recommends measuring an existing bra or briefs and comparing with their measurements for a more accurate indication of your best size, rather than measuring your body. 

Translucent bra

S 55-64cm band under bust (unstretched) and accommodates A-B cup
M 58-66cm band under bust (unstretched) and accommodates B-D cup
L 66-75cm band under bust (unstretched) and accommodates B-D cup
XL 68-78cm band under bust (unstretched) and accommodates B-D cup

Translucent brief

S 68cm width across the hip (unstretched)
M 71cm width across the hip (unstretched)
L 78cm width across the hip (unstretched)
XL 83cm width across the hip (unstretched)