Are a way to simplify the process of making bra size conversions between brands using simple cup counting.

The goal is to address the confusion between how different brands use different letter sequences for their bras in their various country conversions. Or to simply tell how many cups bigger is a bra to another when you don't know how that brand does cup sizing.

How Index sizing can help
How to use Index sizing
How they are constructed
Benefits
Caveats
On Bratabase
Introductory blog post

How Index sizing can help

When you want to buy a bra in a brand you’ve never tried before and wondered what size to start with or if your “usual size” would be in the right ballpark? It can be a stressful and time consuming experience. Skipping cups, adding letters and being inconsistent with labeling is a crime that many bra manufacturers are guilty of.

There is no universal bra size system or conversion chart that covers multiple brands in every market. Recognizing the absence of this very useful resource, here at Bratabase, we’ve developed a way to sort the bras in our database into groups called index sizes. The advantage to this system is that it eliminates the confusion involved with having to figure out equivalent sizes across many well known and even lesser known brands. Cup indexes enables you to navigate through different brands using the UK bra size you are familiar with as the reference point.

How to use Index sizing

On Bratabase you can access the Cup Indexes chart from the Browse heading and then selecting to browse By Size. You will arrive at the chart below. Locate your the UK size you usually buy and arrive at the corresponding Cup Index. If you are a UK 32F, your cup index is 32:7. This means it’s the 7th cup in a 32 band.

If you know exactly which bra you would like to look at, you can browse By Brand to search for the model you wish to see. To browse By Size, simply click on your index size to get a list of results from different brands and models displayed in their native size.

How they are constructed

Index sizes use the standard UK/US band system, but use numbers 1, 2, 3, 4 for cups starting at A cups as index 1.

A = 1
B = 2
C = 3
... and so on

An index size separates bands and cups using the : symbol, examples:

34:8
28:13
36:3

Benefits

Once you know the index size for two bras you can easily know how many cups difference they have by just subtracting the numbers.

Caveats

One important consideration to have when using index sizes, is that some brands will use a different increment to cut their different cups.

Most brands will normally use a 1" difference between cup and cup size. So comparing all those should be alright.

A few brands will use a 2cm difference, or some others will use a 4cm difference (Avocado lingerie ) so it is impossible to make an easy comparison between those bras and others.

The best way to overcome this problem is to just do a proper comparison by measurements.

On Bratabase

Here on Bratabase we will configure each brand manually to set its index sizing according to the sizing information we can collect from the official manufacturer's website.

For most brands you should be able to see next to its size ranges, the number cup indexes.

Browse by size

When browsing bras by size, we will use Index sizing to overcome all the cup difference between manufacturers:

http://www.bratabase.com/browse/by-size/

Comparing brands

When doing a side by side comparison of brands. We will use their index sizes to match up their size ranges. Please consider the aforementioned caveats.

Searching

Simply enter a search for your index size, e.g. “ 32:7 ” (without the quotation marks). If you are unsure of band size or would like to display a range of band sizes in your search results, the search feature is also enabled for this. Entering “ :7 “ will display all the sizes in the 7th cup regardless of band.

This also works on listings search.

Introductory blog post

Index sizing was introduced on Bratabase in March 2014: http://www.bratabase.com/blog/2014/mar/09/introducing-cup-indexes-243/