38DDD Bra Size
38DDD fits a 37–39 inch (94–99 cm) underbust and a full bust of about 45 inches (114 cm). Its sister sizes are 36G and 40DD.
Last reviewed on 25 September 2026.
38DDD at a glance
| Underbust (band) | 37–39 in · 94–99 cm |
|---|---|
| Full bust | ≈ 45 in · 114 cm |
| Bust minus underbust | ≈ 7 in · 18 cm |
| Sister sizes (same cup volume) | 36G · 40DD |
| UK / EU / FR / AU | 38E · 85F · 100F · 16E |
| Same size in US | 38F |
| One cup bigger | 38G |
| One cup smaller | 38DD |
| Approx. top size | L–XL · UK 14–16 / US 10–12 |
Measurements for 38DDD
38DDD is built for an underbust ribcage measurement that falls in the 37–39 inch range, with a full-bust measurement around 45 inches. The band number — 38 — is a mid-range band where the most common fit issue is the band riding up because it has stretched. 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.
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38DDD in Other Sizing Systems
EU, FR, and JP sizing read the band in centimetres, which is why 38DDD maps to 85F (EU), 100F (FR), and 85F (JP) — the same body, expressed in different units. AU sizing uses a small numeric scale (16E for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 38DDD reads as 38E on a UK label.
Is 38DDD the same as 38F or 38E? In US sizing, yes to 38F: the cup letters go AA, A, B, C, D, DD, DDD, then G, and many US retailers print this cup as "DDD/F" — 38F and 38DDD are the same size. In UK sizing the same cup is called 38E, and in EU sizing it is 38F with a centimetre band. A UK 38F is one cup bigger — it matches a US 38G.
Sister Sizes for 38DDD
These sizes have the same cup volume as 38DDD. 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 38DDD 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 38DDD
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 38DDD 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 38DDD 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 38DDD is right for you.
38DDD — frequently asked questions
What measurements are a 38DDD bra in inches and cm?
A 38DDD bra fits an underbust (ribcage) measurement of roughly 37 to 39 inches (94–99 cm) and a full-bust measurement of about 45 inches (114 cm). The cup letter DDD reflects the roughly 7-inch (18 cm) difference between those two numbers.
What size is equivalent to 38DDD? (sister sizes)
The sister sizes of 38DDD are 36G (tighter band, one cup letter up) and 40DD (looser band, one cup letter down). They hold the same cup volume as 38DDD on a different band. Try a sister size when the cups of your 38DDD fit but the band feels too loose or too tight.
What is 38DDD in UK, EU, and other sizing systems?
38DDD (US) converts to 38E in UK sizing, 85F in EU sizing, 100F in French sizing, 16E in Australian sizing, and 85F in Japanese sizing. The body is the same; only the labelling system changes.
Is 38DDD a small or large bra size?
In terms of how common it is, this size pairs an above-average 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 fuller end.
Is 38DDD a small, medium, large, or XL?
As a rough guide, a 38 band usually matches size L–XL in tops and bralettes — around UK dress size 14–16 (US 10–12). The band number drives this more than the cup letter, so 38DDD lands in the same letter size as other 38-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 38DDD?
Keeping the same 38 band, one size up in the cup is 38G, and one size down is 38DD. If you want a bigger or smaller band but the same cup volume, use a sister size instead: 36G or 40DD. Remember that the cup letter is relative to the band — 40DDD has more cup volume than 38DDD, not the same.
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