This Bra-Size Calculator Is a Thing of Genius

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Once you’ve done the band, then you want to measure the fullest part of your bust. Gently take the tape measure and measure it in inches as well.

Then comes the slightly tricky bit: To work out what your cup size is, you want to subtract your band size from your bust size. From the difference between the two sizes, you can work out your cup. If the difference is less than 1, then it’s AA, 1 means A, 2 means B, 3 means C, 4 means D, 5 means DD, and so on.

You’ll still need your band measurement to give you the number preceding the letter. For example, if your band size is 34 but your bust size is 37, then your bra size is 34C (difference of 3, again, means it’s a C cup). Of course, it’s worth mentioning that bras can fit differently according to different brands, but now you have the basic tools to work out your correct size.

If you need more guidance, however, I also spoke to bra-fit expert Julia Mercer from M&S, who gave me some further insights so that if you ever want to know how to find the right size, you’ll be in no doubt. First off, Mercer said that as the average bust size of women is growing (34B to a 36D/36DD in the last decade), “it’s become more important than ever to wear a bra for both comfort and support.”

Mercer also said, reassuringly, that you should “never be alarmed if you have to go up a cup size,” as this will help your posture. And the best way to check if your bra is fitting correctly? “Lift up your arms twist your body, and the bra will fit perfectly in place,” she advises. For more help, keep scrolling for a bra-fitting checklist.