With all the attention that’s been given to finding the right bra fit over the last few years, you’d think by now we’d all be measured up and kitted out with perfectly fitting cups.

But in 2014, Triumph International ran a global survey of 10,000 women and discovered that 64 percent were wearing the wrong bra size. Granted, things have improved slightly since the 2004 survey done by Wacoal America, which found this percentage to be 80. But considering that’s only a 16 percent change in the space of 10 years, something is still going a little haywire in the measuring and fitting department.

Before we get to the actual measuring, it’s helpful to understand what women look for when choosing a bra and why they are putting up with the wrong size.

In the Triumph study, 68 percent of women said they choose underwear to complement the clothing they wear. But more than 64 percent said they struggle to find a bra that fits, with an even higher number admitting that ill-fitting lingerie can ruin their day. (There’s nothing like a bit of pokey underwire to put you in a bad mood, right?)

Then there are women who purposefully choose to wear the wrong size in the hope that a different cup size might enhance their décolletage, whether they want to look more busty or more petite. The most common mistake women are reportedly making is choosing a cup that’s too small and a band that’s too big.

If your bra straps often slip down, if the bra’s band slides up your back, or if the cup’s underwire doesn’t sit properly against your skin, chances are you are wearing the wrong size. 

This can lead to skin irritation and pain, especially for big-busted women who could be experiencing too much weight placed on their shoulders and back. A lack of support can cause sagging, while cups that are too small and wires that dig into the breast can even cause breast tissue to become displaced!

Although there are several lingerie shops that offer a fitting service these days, there have also been many reports of stores implementing incorrect measuring techniques. All the more reason to learn how to measure yourself. You simply need a fabric tape measure and a mirror, and it’s best to do it sans bra. Note that you’ll be working in inches.

Measure your band size. Wrap the tape around your torso, just below your breasts, holding it firmly yet comfortably against your skin. The number in inches is your underbust or band measurement (for example, the ‘34’ in ‘34C’). Round it up or down to the nearest even number. If your number is an uneven number (for example, 35), you might want to try a band size that’s both one below and one above your number.

Measure your cup size. Bend over so that your chest is parallel to the ground and wrap the tape around the centre of your bust, ensuring it’s straight and not too tight. (You can do this while standing upright too, but bending over is a fairly modern method that ensures you are including all your breast tissue in the measurement.) Now for a bit of maths: subtract your band size from the bust measurement. For example, 38-34=4.

To work out your cup size, simply match the small number to its place in the alphabet. So, in this example, the number 4 represents D, and the bra size would be 34D. Here’s a handy table to help you figure out the final step:

Less than 1 inch = AA1 inch = A2 inches = B3 inches = C4 inches = D5 inches = DD