What’s the deal with “sister-sizing”?

What even is “sister-sizing”?! It’s the key to bra-shopping by yourself! Having this knowledge will change the way you look for bras, and give you that almighty confidence that we all lack when it comes to bra-shopping! It’s by far the hardest thing for people to get their head around, but the most important information I want to pass on to my clients. 

Here we go.

  Sister-sizes are bra sizes that carry the same cup volume.

  The cup size and the back size of the bra are relative to each other.

  The cup sizes by themselves don’t have meaning until they’re coupled with a back size measurement!

Here’s the rule:
When you go down in the back size the cup size goes up.
When you go up in the back size, the cup size goes down.

For example:

If you’re wearing a 34E but want a tighter back, 32E is NOT the equivalent size. It’s 32F.

Think of your perfectly-fitting bra like an old-school weighing scales – when you change one size, the other size has to change in order for it to balance out.

If you went to a shop and took a 30E 32E 34E 36E 38E off the rack, you’d find that the cup sizes are all different- they all hold a different volume of breast tissue.

However, a 30E 32DD 34D 36C 38B will all look the same in the cup! 🤯

Have a look at the sister-sizing chart below. I hope it helps!

Remember that:
moving across a row = changing the back band size.
moving up and down a column = changing the cup volume. 

When can I use this info?

Like a lot of clothing, bras may fit you differently depending on the manufacturer. For example, you might find that a particular brand always comes up tighter in the back. Sister-sizing comes in handy here. If your size is a 32G, then you know to try on a 34FF in that brand. Or maybe the shop doesn’t stock your size 30E, so you buy a 32DD and start wearing it on the middle or tightest hook. Buying online? Get your sister-sizing chart out to help you navigate which sizes you want to try!

If you realise that your regular shops don’t stock the right sizes for you, have a little look online to find some independent lingerie shops that offer bigger cup or smaller back sizes – you might be surprised at what you find! Remember: your body and your boobs are not ‘wrong’ or ‘awkward’ or ‘different’. The solution is out there for you!

The Boob Whisperer – Looking fab – Illustration by In The Nud