30DDD Bra Size
30DDD fits a 29–31 inch (74–79 cm) underbust and a full bust of about 37 inches (94 cm). Its sister sizes are 28G and 32DD.
Last reviewed on 25 September 2026.
30DDD at a glance
| Underbust (band) | 29–31 in · 74–79 cm |
|---|---|
| Full bust | ≈ 37 in · 94 cm |
| Bust minus underbust | ≈ 7 in · 18 cm |
| Sister sizes (same cup volume) | 28G · 32DD |
| UK / EU / FR / AU | 30E · 65F · 80F · 8E |
| Same size in US | 30F |
| One cup bigger | 30G |
| One cup smaller | 30DD |
| Approx. top size | XS · UK 6–8 / US 2–4 |
Measurements for 30DDD
30DDD is built for an underbust ribcage measurement that falls in the 29–31 inch range, with a full-bust measurement around 37 inches. The band number — 30 — is a smaller band that needs to sit firmly without cutting in. The cup letter — DDD — describes the difference between the two measurements; a DDD cup (US) means the full bust is about seven inches larger than the underbust — this is where US notation diverges from UK, where the same volume is called an E cup. Many US labels print it as DDD/F.
Shop 30DDD Bras
Confident 30DDD is your size? See what's available in it right now — sorted by style.
Shop All 30DDD Bras on AmazonAs an Amazon Associate, BraCalc earns from qualifying purchases — at no extra cost to you.
30DDD in Other Sizing Systems
EU, FR, and JP sizing read the band in centimetres, which is why 30DDD maps to 65F (EU), 80F (FR), and 65F (JP) — the same body, expressed in different units. AU sizing uses a small numeric scale (8E for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 30DDD reads as 30E on a UK label.
Is 30DDD the same as 30F or 30E? In US sizing, yes to 30F: the cup letters go AA, A, B, C, D, DD, DDD, then G, and many US retailers print this cup as "DDD/F" — 30F and 30DDD are the same size. In UK sizing the same cup is called 30E, and in EU sizing it is 30F with a centimetre band. A UK 30F is one cup bigger — it matches a US 30G.
Sister Sizes for 30DDD
These sizes have the same cup volume as 30DDD. Try them if the band feels too tight or too loose.
← Tighter band, bigger cup · Looser band, smaller cup →
Sister sizes are useful when the cup of your 30DDD fits well but the band is wrong — too loose by the end of the day, or too tight to clip up comfortably. Going one band smaller and one cup larger keeps the cup volume the same while tightening the band; going the other way loosens the band without losing cup space. Read the full sister-size matrix if you want to see how this works for every size at once.
Fit Tips for 30DDD
DDD (often labelled DDD/F in US sizing) benefits from full-coverage cups and three-part construction that offers more structure. Side support panels help redirect tissue forward and reduce side spillage.
If your 30DDD bra is gapping at the top of the cup, the cup may be too large or the wrong shape — try a demi-cup or balconette before assuming the size is wrong. If the centre piece between the cups (the gore) does not lay flat against your sternum, the cup is almost certainly too small; go up one cup. If the band rides up across your back during the day, the band has stretched out or was too loose to begin with — drop one band size and add one cup to keep the same cup volume.
For more detailed troubleshooting, the Fit Test on the home page covers six common visible problems and the size or shape change that usually addresses each one. The guide to measuring mistakes covers the most common reasons a calculation comes out wrong in the first place.
Related sizes
If 30DDD is close but not quite right, these neighbouring sizes are the most useful next places to look:
See every size at a glance on the full bra size index, or read how to measure your bra size if you are not sure 30DDD is right for you.
30DDD — frequently asked questions
What measurements are a 30DDD bra in inches and cm?
A 30DDD bra fits an underbust (ribcage) measurement of roughly 29 to 31 inches (74–79 cm) and a full-bust measurement of about 37 inches (94 cm). The cup letter DDD reflects the roughly 7-inch (18 cm) difference between those two numbers.
What size is equivalent to 30DDD? (sister sizes)
The sister sizes of 30DDD are 28G (tighter band, one cup letter up) and 32DD (looser band, one cup letter down). They hold the same cup volume as 30DDD on a different band. Try a sister size when the cups of your 30DDD fit but the band feels too loose or too tight.
What is 30DDD in UK, EU, and other sizing systems?
30DDD (US) converts to 30E in UK sizing, 65F in EU sizing, 80F in French sizing, 8E in Australian sizing, and 65F in Japanese sizing. The body is the same; only the labelling system changes.
Is 30DDD a small or large bra size?
In terms of how common it is, this size pairs a small band with a fuller-bust cup. There is no universal "small" or "large" bra size — the same cup letter describes a different volume on every band — but within the full range BraCalc covers (bands 28–48, cups AA–H) this combination sits toward the compact end.
Is 30DDD a small, medium, large, or XL?
As a rough guide, a 30 band usually matches size XS in tops and bralettes — around UK dress size 6–8 (US 2–4). The band number drives this more than the cup letter, so 30DDD lands in the same letter size as other 30-band bras. With a fuller cup, many people go one size up in fitted tops so the bust has room. Letter sizing varies a lot between brands, so always check the brand's own chart.
What is the next size up or down from 30DDD?
Keeping the same 30 band, one size up in the cup is 30G, and one size down is 30DD. If you want a bigger or smaller band but the same cup volume, use a sister size instead: 28G or 32DD. Remember that the cup letter is relative to the band — 32DDD has more cup volume than 30DDD, not the same.
Not sure about your size? Measure yourself and double-check.
Calculate My SizeAlready sure? Shop 30DDD bras on Amazon →