Measure around your rib cage, just under the breast. The tape measure should feel snug. Round up to the nearest centimetre and refer to the table for your Back Size.
Overbust Measurement to Calculate Cup Size
Measure around the bust at the fullest point of the breast. Round up to the nearest centimetre. To calculate your cup size subtract the Underbust measurement from the Overbust measurement and refer to the table for your Cup Size.