"What you may not realise is that you should actually have bras in lots of different sizes stashed away in your wardrobe. As much as you may want to find your one, true size to make bra shopping a breeze, in reality different brands and different bra styles mean you’ll need to be willing to be a bit flexible when it comes to those numbers. The important thing, as always, is the fit, so don’t get hung up on what you think is your size – let your boobs tell you whether the bra is right or not!
When you’re trying on bras, the first thing to consider is the bra band. Is it too tight? Does it ride up? Try it on the loosest hooks; if it doesn’t sit firmly and horizontally across your back, you’ve probably picked up the wrong size – even if it is your usual. Adjusting your size can help you find the best fit – so go up or down a band size as necessary.
At this point, it’s time to use the bra size table to your advantage. Moving diagonally across the table will give you other options to try out if you’ve spotted a bra you like but it just isn’t working for you in your regular size. Not all D-cups (or E-cups, or F-cups…) are the same; in fact, the size of the cup is related to the size of the band. So if you drop a band size, go up a cup size (or vice versa) and you might find your perfect match! If you usually wear a 36D, for example, but need a tighter band, try a 34E on for size.
There are lot of different factors which will determine if you need to change your size; the brand you’re looking at might use a thicker underwire which digs in at your normal size, for example. The style of the bra can also affect what size you’ll need. Just remember to be flexible, and if it doesn’t feel right, don’t buy it!"
Excerpted from "The Bra Size Chart Explained"