34C Sister Sizes

The sizes in bold are the ones to use. The outer two share the cup volume in theory, but are proportioned for a noticeably different frame.

When to choose 32D

Choose 32D if the 34 band rides up your back, or if you are fastening a fairly new 34C on its tightest hook. This is the more common move, because 34 is the band many people are given by default when a 32 would fit their ribcage better.

When to choose 36B

Choose 36B if the cups of your 34C fit but the band digs in on the loosest hook. Before you do, check that you are not spilling out of the cups, because cups that are too small make a band feel tight.

What a 34C measures

All three sizes are designed around a bust of about 37 inches. The difference is how much of that total is ribcage and how much is breast, which is why the band changes and the cup letter moves the other way.

All three sizes are stocked by virtually every UK bra retailer, so this is one of the easiest families to try side by side in a shop.

If neither sister size works

Sister sizes only help when the cup volume is already right. If you spill out of a 34C or the cups gape, keep the 34 band and change the cup letter. If you are unsure which problem you have, when to sister size up or down will help you decide, and the calculator will give you a fresh starting size from your measurements.

Frequently asked questions

What is the sister size of a 34C?

32D on a firmer band and 36B on a looser band. Both have the same cup volume as a 34C.

Is a 32D the same as a 34C?

The cups hold the same volume. The 32D has a band one size smaller, so it fits more firmly around the ribcage.

Can I wear a 38A if I am a 34C?

That is two steps away. The cup volume is the same on paper, but the wires, straps and proportions are made for a larger frame, and the band will be four inches longer. It is unlikely to support you well.