Sister sizes? The industry’s best kept secret.

We recognise shopping for bras isn’t always easy. ‘What cup size is best?’ ‘What band works?’ ‘How do I know if this bra fits?’ We get it, it can be complicated.

There is one way to make it easier though – sister sizing. You may have heard this term before and once you get to grips with it, it can be a useful trick to have up your sleeve when searching for a good fit.

Let’s say you’re a 34DD, but the bra you’ve got your eye on is sold out. Alternative options would be a 32E or a 36C in sister sizing.

The rule to sister sizing is:

You go one band size down and one cup size up

Or one band size up and one cup size down

Think of sister sizing as a sliding scale, with the added bonus that both of those options will fit (provided you have your original size right!).

You might be thinking ‘how is this possible’? Well, when bras and made they go through a process called grading. Essentially this is what scales the size of a bra to ensure that the range fits correctly.

The graph below will help you visualise how each row is a family of sister sizes, all of which will work for you. However, our top tip would be to only go a couple of band sizes either way.

Start by finding your true size and then move right to left horizontially to find your sister sizes.