Bra Size Myths Debunked

1. "You should add four inches to your underbust"

Not with modern bras. The rule dates from non-stretch fabrics. A University of Portsmouth study found the traditional method overestimated band size in 76% of the women tested and underestimated cup size in 84%. Use your real underbust measurement. Full story: why the +4 method is wrong.

2. "A D cup is big, and DD is huge"

They are mid-range sizes. D is the fifth of seventeen UK cups and DD the sixth. The reputation comes from the days when shops stopped at DD. See is DD a big cup size?

3. "The cup letter tells you how big the breasts are"

Only together with the band. A cup letter is the difference between bust and band. A 30D and a 38D are both a four-inch difference, and the second holds far more. A 30F and a 36D hold the same.

4. "You are the same size in every shop"

There is no enforced standard. Each brand cuts to its own patterns, and styles within a brand differ. Your size is where you start in a new brand. See how accurate bra size calculators are.

5. "Once you know your size, it is your size for life"

It changes. Weight, hormones, pregnancy, age and exercise all move it. Check once a year. See can your bra size change?

6. "The straps hold your breasts up"

The band does most of that. Straps keep the cups in place. If your straps dig in, the band is too loose. See bra straps digging into your shoulders.

7. "If it feels tight, go up a band"

Often the cups are the problem. Cups that are too small push the bra off your chest and tighten the band. Going up a band then gives you a loose band as well. See do I need a bigger cup or a smaller band?

8. "A new bra should fit on the tightest hook"

The loosest. Bands stretch with wear, and the tighter hooks are there to take up the slack later. See how tight a bra band should be.

9. "DD is bigger than E", and "a UK F is the same as a US F"

Neither is true. In the UK the order is D, DD, E, F, FF, G. And UK and US letters differ above DD: a UK F is a US G. See is DD bigger than E? and UK vs US bra sizes.

10. "A calculator or a tape measure gives you your true size"

It gives you a starting size. Measurements cannot see breast shape or how a brand cuts. The size is confirmed by how the bra fits on your body. That includes our own calculator.

A few health myths

"Wearing a bra stops your breasts sagging"

There is no reliable evidence either way. Bras support and shape while you wear them. Long-term changes in the breasts are driven mainly by age, genetics, weight change and pregnancy.

"Underwired bras cause breast cancer"

No. Cancer charities are clear that there is no good evidence that bras of any kind cause cancer.

"Sleeping in a bra is bad for you"

It is a matter of comfort. There is no good evidence of harm from sleeping in a soft, well-fitting bra, and none of benefit either.

"You must wear a bra"

You do not have to. Wear one if it makes you more comfortable, for support during exercise, or because you like to.

"The famous statistic proves most women are in the wrong bra"

The figure comes from small studies of particular groups. It points to a real problem and cannot be treated as a precise number. See do 80% of women wear the wrong bra size?

Frequently asked questions

What is the biggest myth about bra sizes?

That the cup letter tells you how big the breasts are. A cup letter only describes the difference between bust and band, so a D on a 30 band and a D on a 40 band are very different volumes.

Does wearing a bra prevent sagging?

There is no reliable evidence that wearing a bra prevents sagging over the long term, or that not wearing one causes it. Changes in breast shape are driven mainly by age, genetics, weight change and pregnancy.

Do underwired bras cause cancer?

No. Cancer research organisations state there is no good evidence linking underwired bras, or bras of any kind, to breast cancer.