We’re often told that many lingerie shoppers are wearing the wrong size bra. Well, according to a new study, the problem might be even worse than previously thought.

Analysing data from 41,380 women, Boux Avenue found that only 19% are wearing the correct bra size. That’s right, a whopping 81% are unknowingly sporting an ill-fitting bra, with 26% wearing a cup size too big.

Both your band and cup can fluctuate with your weight and be affected by things like hormones and exercise. Sometimes it’s clear when a bra doesn’t fit – the straps dig in painfully or you get that bulging ‘double boob’ overspill effect, for example. But it’s not always obvious.

According to underwear experts, there are five elements you need to check to find the perfect fit…

1. Underband

First, check how the bottom of the bra sits against your ribcage.

“The underband should fit parallel to the front of the bra at the back, and you should be able to slightly pull the underband away from the body, without there being too much stretch,” says Lee-Anne Norton, L&D business partner at Boux Avenue, which offers a fitting service in 30 of its UK stores.

This is crucial in terms of support, says Michelle Piercy, fit specialist at Pour Moi, which has introduced virtual fittings via its website: “Underbands hold 80% of the weight of your breasts, if your band gets too loose over time, the weight of your breasts will make the back ride up.”

2. Straps

“Shoulder straps play a vital role in supporting the weight of your breasts,” says Piercy, which is why it’s important the straps don’t slip down all the time. “But the elastic doesn’t last forever. Bras that feature fully adjustable straps will help, but once the elastic has gone they won’t offer sufficient support.”

On the other hand, straps that are too tight “could be a sign that your band isn’t giving you the support you need,” says Norton. “Of course, if your bra straps do keep falling down you might just need to adjust them, but if they still aren’t sitting right you might need to check your sizing and find out which bra style is best for you.”

3. Wires

If you’re wearing an underwired bra, it should sit snuggly against the skin but not too tight.

Norton says: “Wires should be resting against the ribcage, and sitting behind the breast tissue under the arm – not digging in!”

4. Cups

“A bra cup should hold all of your breast tissue and sit smoothly on your body as gaps will ruin the line of your clothing,” says Piercy.

The cup should “fit comfortably…without overspill, which means the cup is too tight,” says Norton. If there’s any gaping it means “you are probably wearing a bra that is too big.”

5. Front

Finally, check the front of the bra right in the middle.

“If your centrefold is standing away from your chest, this can be a sign your cup size is too small,” Norton says. “If you find it is digging in, it could be the band size that is too small.”