Last updated: August 2026
A P cup is a US/European cup size. Here is what it means, the closest US label, and real measurements across common bands.
What a cup letter actually measures
A cup letter is not a fixed amount — it is the difference between your bust and your underbust, at roughly one cup per inch. That is why a cup letter always travels with a band, and why the same letter is a different real-world size on a 28 band than on a 40 band.
The US vs UK ladder — why P can mean two things
Below a D cup, the US and UK count cups the same way. Above D they diverge: the UK inserts single letters (DD, E, F, FF, G, GG…) while the US doubles and skips (DD, DDD, then G, H, I…). Because they climb the ladder at different rates, one letter can sit at a different rung — and therefore a different cup volume — in each system.
P cup in US, UK and EU
| System | Cup label | Bust − underbust |
|---|---|---|
| US | P | ≈ 16 in (41 cm) |
| UK | KK (nearest) | ≈ 16 in (41 cm) |
| EU | P | ≈ 16 in (41 cm) |
UK sizing writes this cup differently — the nearest UK label is KK.
Example P cup bra sizes
Approximate measurements for a P cup across common bands:
| Full size | Underbust | Bust |
|---|---|---|
| 28P | 27–28 in | 44–45 in |
| 30P | 29–30 in | 46–47 in |
| 32P | 31–32 in | 48–49 in |
| 34P | 33–34 in | 50–51 in |
| 36P | 35–36 in | 52–53 in |
| 38P | 37–38 in | 54–55 in |
| 40P | 39–40 in | 56–57 in |
How P cup looks on different bands
Because the cup is a difference, a P on a small band and a P on a wide band are not the same volume — the wider band starts from a bigger bust, so the cup holds more. This is why ‘what does P cup look like’ has no single answer: it depends entirely on the band it rides on. If a P looks too big or too small, the fix is often a change of band, not cup.
How to check the fit is actually right
Numbers get you to the right size on paper; these hands-on checks tell you whether it fits in real life. Do them in front of a mirror, wearing the bra on the loosest hook:
- Band: it should sit level all the way around, in line with the front. Slide two fingers under it at the back — snug, not loose, no riding up when you raise your arms. The band does roughly 80% of the support work, so this matters most.
- Cups: do a quick “scoop and swoop” — lean forward, settle everything into the cup, then stand up. There should be no spillage over the top or sides, and no wrinkling or gaping at the edge. Spillage means size up a cup; gaping means size down a cup.
- Centre gore: the little bridge between the cups should lie flat against your breastbone. If it floats off the body, the cup is usually too small.
- Straps: you should fit a finger under them comfortably. If they dig in or carry most of the weight, the band is too loose — tighten it or size the band down.
Finding P cup bras
P is a fuller cup, so everyday high-street ranges carry fewer options. Specialist fuller-bust retailers stock far more, and knowing your sister sizes (a band up and cup down, or band down and cup up) widens what you can wear when stock is limited.
Is P cup big?
A P cup means a bust roughly 16 inches bigger than the underbust. That is in the very full range. But remember the letter rides with its band, so the honest answer to ‘is P big’ is always ‘on which band?’.