K Cup Size (UK)
A UK K cup is a bust measurement 15 inches larger than the band, the fifteenth and usually last position on the UK ladder. A US K is the eleventh position, four cups smaller; the UK K is an EU O.
What is a K cup?
A K cup in UK sizing means the fullest bust measurement is 15 inches (≈ 38 cm) larger than the underbust band. In US sizing the same 15-inch difference is labelled beyond K (US K is the 11th position); in EU sizing O. It is not a fixed volume: what the cup holds grows with the band it sits on.
Same letter, nine volumes. A 28K and a 44K are both “K cups”: the second holds several times the volume of the first.
Every K-cup size
The same 15-inch difference on each band. Read across for measurements, sister sizes and the EU / FR / AU labels; tap a size for its full guide.
| Size | Underbust | Bust | Sister sizes | EU · FR · AU |
|---|---|---|---|---|
| 28K | 27–28″ · 69–71 cm | 43″ · 109 cm | — · 30JJ | 60O · 75O · 6K |
| 30K | 29–30″ · 74–76 cm | 45″ · 114 cm | — · 32JJ | 65O · 80O · 8K |
| 32K | 31–32″ · 79–81 cm | 47″ · 119 cm | — · 34JJ | 70O · 85O · 10K |
| 34K | 33–34″ · 84–86 cm | 49″ · 124 cm | — · 36JJ | 75O · 90O · 12K |
| 36K | 35–36″ · 89–91 cm | 51″ · 130 cm | — · 38JJ | 80O · 95O · 14K |
| 38K | 37–38″ · 94–97 cm | 53″ · 135 cm | — · 40JJ | 85O · 100O · 16K |
| 40K | 39–40″ · 99–102 cm | 55″ · 140 cm | — · 42JJ | 90O · 105O · 18K |
| 42K | 41–42″ · 104–107 cm | 57″ · 145 cm | — · 44JJ | 95O · 110O · 20K |
| 44K | 43–44″ · 109–112 cm | 59″ · 150 cm | — · — | 100O · 115O · 22K |
The K cup, in numbers
Volume is the pairing, not the letter. At 15 inches of difference the cup is beyond the range the clinical weight studies covered, so this site does not print a weight; on a 34 band its sisters are — and 36JJ.
Is a K cup big?
Fifteen inches of difference is the top of the widely manufactured range and beyond the clinical weight studies this site cites. It is a size the mass market has never stocked and the UK specialists cut on select styles; above it, made-to-order.
A UK K on a 30 band and a US K on a 30 band are different bras, and a shopper moving between the two markets must convert by position or buy four cups wrong.
Key takeaway: “K cup” describes a 15-inch difference in UK letters. Volume depends on the band; convert by position, never by letter.
What people get wrong about K cups
Measured K, sold something else?
Add-inches charts cannot produce a K: they inflate the band and hand the wearer a larger cup that stands off the chest. Measured snugly, the band is right and the cup comes from a specialist.
K cup in US, EU and other systems
4″ difference. Matches UK and EU letters.
Identical to US. Full-bust specialists (Panache, Freya, Curvy Kate) label in UK letters.
Identical to US. FR, IT, DE and JP use EU cup letters.
Convert any exact size with the size converter.
Bra styles that fit a K cup
Seamed, side-supported full cups on wide, firm bands, and longlines. Availability is by style rather than by brand; check the size selector.
Frame like a 28 band, also look for narrower wires and shorter straps The same K cup is deeper and narrower here.
The widest choice of styles at this cup. Molded for a smooth line, seamed for shape and lift.
The K cup is wider and shallower; prioritise a firm, wide band and a wire that fully encloses the root. Longline and three-hook styles help.
Shape matters as much as size: see the fit guide for the five breast shapes and the constructions that suit each.
K cup: answered
How big is a UK K cup?
A UK K cup is a bust 15 inches (38 cm) larger than the band, the fifteenth UK cup letter. A US K is the eleventh position, so the two are four cups apart. The EU equivalent is O.
Is a UK K the same as a US K?
No. A US K is eleven inches of difference, which is a UK H. A UK K is fifteen inches. Convert by position, never by letter.
What comes after K?
In UK notation KK, then L, LL and onward, cut by a few specialist labels and otherwise made to order. K is where most ranges stop, not where sizing stops.
What are the sister sizes of a 34K?
A 32KK and a 36JJ in UK letters.
Which brands make UK K cups?
Panache, Elomi, Curvy Kate and Fantasie on select styles; Parfait reaches a K in US letters (the eleventh position) on select styles, which is a different cup.
Opens HauteFlair’s own hub page; use your measured size there. HauteFlair is owned by the same company as Brasize.ai; that relationship never changes the sizing math, charts, or fit advice on this page. How this site makes money.
Find your exact size
A cup letter is only half the answer. Two measurements give you both halves.
Calculate My Bra Size →