What the number means
A UK band size is a length in inches. It corresponds to the measurement around your ribcage directly under your bust, rounded to the nearest even number. It has nothing to do with your bust measurement, your dress size or your back width across the shoulders, although shops often call it "back size".
Why the band matters most
A bra supports from below. The band grips the ribcage and the cups are held up from it. Fitters commonly say the band provides most of the support, with the straps there to keep the cups in place. For that to work, the band has to be firm enough to stay level without help.
When the band is too big, the rest of the bra cannot do its job, and most familiar complaints follow: the back rides up, the straps dig in, the wires shift. This is why every fit check starts with the band.
Band and cup are linked
The cup letter is measured relative to the band. Change the band and the cup changes with it, even if the letter stays the same.
| If you go from 34D to | The band is | The cup volume is |
|---|---|---|
| 36D | Longer | Bigger |
| 36C | Longer | The same |
| 32D | Shorter | Smaller |
| 32DD | Shorter | The same |
Sizes that keep the cup volume while changing the band are called sister sizes. See what sister sizes are.
The hooks
Most bras have three rows of eyes, about half an inch apart. They are there to keep the bra wearable as its elastic relaxes, and not to make one bra fit three sizes of person.
- Loosest row: where a new bra should fit firmly.
- Middle row: after a few months of wear.
- Tightest row: towards the end of the bra's life.
A new bra that only feels secure on the tightest row is a band size too big. When the tightest row no longer holds, the bra needs replacing.
How to find yours
Measure snugly under the bust and round to the nearest even number. The table of ranges is in what band size am I?, and the measuring technique in how to measure your underbust. Then confirm it on your body with the tests in how tight a bra band should be.
Guides to each band
Who needs a 28 band, which brands make them and where to buy.
Band Guide 30 Band Bras in the UKWhy the high street rarely stocks a 30 band, and where to find one.
Band Guide 32 Band Size GuideWho a 32 band fits, the sizes it comes in and its sister sizes.
Band Guide 34 Band Size GuideThe most commonly sold band: who it really fits and when to try a 32.
Band Guide 36 Band Size GuideMeasurements, sister sizes and fit notes for a 36 band.
Band Guide 38, 40 and 42 Band Size GuideFitting larger bands: what gives support and where the range is widest.
Bands in other countries
US bands use the same numbers as UK bands. European bands are in centimetres (a UK 34 is a 75), French and Spanish bands are 15 higher than European ones (90), and Australian bands use dress sizes (12). The international bra size chart converts them all.
Frequently asked questions
What does the band size number mean?
In UK and US sizing it is the band length in inches, matched to your ribcage measurement under the bust and rounded to an even number. A 34 band is for a ribcage of about 33 to 35 inches.
Why do band sizes only come in even numbers?
By convention. The hook-and-eye fastening gives about an inch of adjustment either way, which covers the odd sizes in between.
Does going up a band size change the cup?
Yes. A 36C has a larger cup than a 34C. To keep the same cup volume when you go up a band, go down a cup letter: 34C to 36B.
Which hook should I fasten my bra on?
The loosest when the bra is new. Move to the middle and then the tightest as the elastic stretches with wear.
Not measured recently? It takes two minutes.
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