A correctly fitting bra is essential for comfort and support and to help promote good posture. An estimated two thirds of women may be wearing the wrong size bra, but a few simple checks can help identify whether you may be one of them.
By far the most common mistake is to wear a bra with too large a band (the band is the part which goes around the body, beneath the breast). The key to a well fitting bra is firstly to ensure you have the correct band size. Many people think a large bust must mean a large band size, but this is not necessarily so. The band is measured around the back, and beneath the breast, and is therefore a measure of the ribcage rather than the bust.
With a correct size bra, the band should sit level all the way round. If it rides up at the back this may mean you are wearing too large a band size. The shoulder straps should be parallel to each-other, or slightly "V" shaped, and should not dig in to the shoulders.
About 80% of the support is provided by the band, and only about 20% by the straps. If the shoulder straps dig in, this may mean that too much support is being provided by the straps, and the band may be too large.
At the front, the centre of the bra (where the cups join) should sit against the body. The underwire should sit flat against the body, in the natural crease below the breast, and should fully encompass the breast. Again, if the front is pulling away from the body, this may mean you are wearing too large a band, and/or too small a cup.
If the underwire has a tendency to slip down, away from the natural crease beneath the breast, this may indicate that the band is too small, thereby causing the underwire to slip down to the narrower part of the rib cage. If the band is too small, it may also cause bulging to the side area.
Having found the correct band size, you should then look at cup size. The breast should be fully encased by the underwire, which should follow the natural crease below the breast. The cups should sit on the breast without gaping, and without the breast bulging over the top. If there is gaping, this may mean the cup is too large. If there is bulging of the breast at the top of the cups, the cups may be too small. Similarly, if there is bulging at the sides of the cups, or if the underwire does not fully encase the breast, this may mean the cup size is too small, although bulging at the sides can also indicate too tight a band.
Relationship of Band Size to Cup Size
It is important to realise that band and cup size are inter-related. The cup on a size 34B is not the same as the cup on a 32B, or on a 36B. Generally speaking, if you reduce the band by one size, you must increase the letter for the cup by one size, to give the same volume of cup. A 34B cup would accordingly have similar volume to a 32C cup. A 36C would have a similar volume of cup as a 34D cup. If you are wearing a 34C and are happy that the cup size fits nicely, but feel that the band is riding up at the back and may therefore be too large, you may wish to try a 32D. Be prepared to be surprised - you may be more busty than you thought!
Nothing can quite compare with the benefit of trying on a few different sizes. Try firstly one size below and above your usual size band to see if you can achieve a better fit. Perhaps the most common mistake is to wear too large a band size. If you go down one band size, don't forget to increase one cup size - and try a couple of cup sizes, too. Don't worry about asking to try on a number of different sizes - all good shops will be happy for you to try on a number of sizes to ensure a good fit.
Don't forget that different manufacturers will also tend to vary slightly in terms of cut and fit, and you may find that one particular brand will suit you the best. It is also important to remember that different styles of bra will sit differently. Different styles of bra are designed to achieve different results - push-up bras will enhance cleavage, whilst soft-cup bras will provide a more natural contoured shape. At the end of the day, the most important thing is that you feel comfortable and confident.