Bra sizing is plagued by myths — ideas that circulate as fact, get reinforced by well-meaning shop assistants and friends, and keep millions of women in bras that don't fit. Some of these myths are relatively harmless misunderstandings. Others actively point women toward the wrong size every time.
Here are seven of the most persistent myths, and the truth behind each one.
"DD is a large cup size"
DD is only the fifth cup size in the US system — A, B, C, D, DD. On a 30 band, a DD cup contains very little volume. On a 44 band, it contains a great deal. Cup size is always relative to the band — a 30DD and a 44DD have almost nothing in common in terms of actual breast volume. The idea that "DD = large" has led countless women with larger band sizes to believe they can't possibly need a cup that large, and so they stuff themselves into a D or C instead. This is one of the most common causes of ill-fitting bras.
"You only need to remeasure after pregnancy"
Pregnancy and breastfeeding cause some of the most dramatic size changes — but they're far from the only ones. Weight fluctuation, hormonal changes (including the menstrual cycle, perimenopause, and contraception), changes in exercise habits, certain medications, and simply ageing can all shift your size without any pregnancy involved. Most experts recommend remeasuring every 6–12 months as a baseline, regardless of whether anything obvious has changed. See our full guide on why bra size changes.
"Add 4 inches to your underbust to find your band size"
This rule originated decades ago when bra elastic was far less stretchy than it is today. Manufacturers instructed women to add 4 inches (or sometimes 5) to their underbust measurement because the elastic didn't stretch enough to accommodate the body without extra room. Modern bra elastic stretches significantly — adding 4 inches to today's bras would produce a band that's far too large to provide any meaningful support. The current method is simple: your underbust measurement in inches, rounded to the nearest even number, is your band size. No addition needed.
"The straps are what hold a bra up"
Straps are for shape and positioning — the band is what provides support. A properly fitted band should provide roughly 80% of a bra's total support. Straps should feel comfortable and stay in place, but if you removed them entirely on a well-fitting bra, the bra should still stay up and feel supportive. If your straps are doing heavy lifting — digging into the shoulders, needing to be fully tightened — it's almost always because the band is too loose. Tightening the straps further is compensating for the wrong problem.
"If it's uncomfortable, you just need to break it in"
A correctly fitting bra should feel comfortable from the first wear. It might feel slightly firm — a new band is at its snuggest before the elastic has been washed and worn a few times — but it should never cause pain, dig in, or leave deep red marks. Discomfort that you're told will "go away once you break it in" usually doesn't go away; it just becomes familiar. Red marks, pain at the underwire, grooves in the shoulders, and a riding band are all signs of a fit problem, not a new-bra problem.
"All bras in the same size fit the same"
A 34C at Victoria's Secret and a 34C at Freya are not the same bra. Every brand uses slightly different block patterns, underwire shapes, cup depths, and grading. Some brands run large in the cup; others have narrow underwires. Finding your correct size is a starting point — you still need to try bras on (or check return policies when shopping online) because fit varies significantly between brands and even between styles within the same brand. Our brand size guide covers specific fitting quirks for 14 major brands.
"You should start on the tightest hook and work outward as the bra stretches"
It's actually the opposite. A new bra should fasten on the loosest hook comfortably. As the bra's elastic loosens over time with washing and wear, you move to progressively tighter hooks to maintain the same fit. Starting on the tightest hook means you have nowhere to go as the bra ages — it will quickly become too loose to provide adequate support. When a bra can no longer provide a snug fit even on the tightest hook, it's ready to be replaced.
Now you know the myths — put the correct method to work. Our free calculator uses your actual measurements to find your real size.
Find My Actual Size →Why These Myths Persist
Most of these myths have been passed down through decades of retail fitting advice that was either outdated (like the +4 rule) or oversimplified for quick in-store fittings. Some persist because they're convenient — "break it in" is easier to say than "this bra doesn't fit you." Others persist because the correct information is less intuitive than the myth: telling someone that DD is a small cup on a small band requires understanding a system that isn't immediately logical.
The solution is straightforward: start with your measurements, use them as a guide, and treat size as a starting point rather than a fixed answer. Our bra fitting guide explains exactly what a correctly fitting bra looks and feels like at each point — so you can assess fit for yourself, without relying on received wisdom that may or may not be accurate.