30 Bra Size: Every Cup on a 30 Band

Fits an underbust of

29-31 in

74-79 cm

Called this elsewhere

EU 65

FR 80 · AU 8 · JP 65

Cup pages on this band

30A through 30F

30 sits in the gap between what specialist brands cut as their starting size and what high street ranges treat as their smallest. It is the band most likely to be stocked in a shop and still not stocked in the cup you need, because ranges tend to pair a 30 band with only the middle of the ladder.

Are you really a 30?

Measure snug and level directly under the bust, with no bra on or a non-padded one, and breathe normally. A reading between 29 and 31 inches (74-79 cm) is a 30 band. Nothing is added to that number: the "+4" rule was written for rigid 1950s fabric and on modern elastic it produces a band about two sizes too loose, which is how the same measurement used to be sold as a 34.

A 29 or 31 inch reading puts you between bands, and the smaller one is the better first try for the same reason: elastic only ever gets slacker. The exception is a 31 with a very firm band brand, where a 32 that fastens on the loosest hook leaves room to tighten later.

If the tape and the tag disagree, the calculator settles it in two measurements, and how to measure covers the technique in detail.

Every 30 size, in every system

Size	UK	EU	FR	AU	JP	KR	Volume
30A	30A	65A	80A	8A	B65	B65	41 cc
30B	30B	65B	80B	8B	C65	C65	163 cc
30C	30C	65C	80C	8C	D65	D65	366 cc
30D	30D	65D	80D	8D	E65	E65	651 cc
30DD	30DD	65E	80E	8DD	F65	F65	1018 cc
30F	30F	65G	80G	8F	H65	H65	1995 cc

Every size in the first column has its own page with sister sizes, a volume comparison and shopping notes. Volumes are estimates from the model on the weight page.

Buying at a 30 band

The 30 band is where sister sizing gets misused: a shop with no 30 will offer a 32 in a smaller cup and call it equivalent. It holds a similar cup volume, but it does not hold the same band tension, which is the part that carries the weight. Treat a sister size as a compromise, not a match.

The fit problem this band produces most

Straps digging is the signature complaint at this band, and it is usually a symptom rather than a cause: a band too loose transfers the load to the shoulders. Tighten the band first and the straps stop being the problem.

Work through it with the fit problem solver, or read the full list of fit problems if you are not sure which one you have.

Why 30D is not the same size as 42D

A cup letter records the difference between bust and underbust, not a volume, so the same letter grows with the band underneath it. On a 30 band, D works out at roughly 651 cc per cup, against 912 cc for 42D - a difference of about 40% from the same letter. Across every band this site charts:

28D · 608 cc30D · 651 cc32D · 695 cc34D · 738 cc36D · 782 cc38D · 825 cc40D · 869 cc42D · 912 cc

This is also why sister sizing works: dropping a band and adding a letter keeps the volume roughly constant. See sister sizes explained for the full ladder.

Sister sizes for every 30

If a 30 band rides up, the sister on the tighter band is the one to try; if it digs, go the other way. Both hold roughly the cup volume you already wear.

Your size	Tighter band (28)	Looser band (32)
30A	28B	not charted
30B	28C	32A
30C	28D	32B
30D	not charted	32C
30DD	not charted	32D
30F	not charted	32DDD

Frequently asked questions

What underbust measurement is a 30 band?

Roughly 29 to 31 inches (74-79 cm) measured snug and level directly under the bust, with no bra or a non-padded one. Modern sizing adds nothing to that number: your band is your measurement, rounded to the nearest even size.

Is a 30 band the same in UK and European sizing?

The UK uses the same 30, but Europe calls it 65, France 80, Australia 8, and Japan and Korea 65. Only the cup letters change further, and they change differently in each system.

Does a 30D mean the same size as a 28D?

No. A cup letter is a difference, not a volume, so it scales with the band it sits on. 30D holds about 651 cc per cup, while 42D holds about 912 cc - roughly 40% different for the same letter. That is why moving a band without moving the letter changes the fit twice over.

I was measured as a 34. Why does this page say 30?

The old fitting method added four inches to the underbust measurement, which was designed for the rigid fabrics of the 1950s. On elastic modern bands it produces a band roughly two sizes too loose, which is how a 29-31 inch underbust ends up in a 34. If you were fitted that way, your real starting size is likely a 30 with a fuller cup letter than you are used to.

Other bands

28 band 32 band 34 band 36 band 38 band 40 band 42 band

Highlighted bands are this one's sister bands: the same cup volume sits on them one letter up or down. Not sure which band you are? Use the calculator.

Last updated August 2026.