It is absolutely recommended to try the bra on in the shop to be sure you find your right fit as these sets are made in small batches with variance within each size, but here's a reference point as a guide :) Pairs perfectly with the Barbara Thong.
XS - 65A/B
S - 70B/C
M - 75B/C
L - 80C/D
XL - 85D/E