38D Bra Size
Everything you need to know about bra size 38D — measurements, sister sizes, international equivalents, and fit advice.
Last reviewed on 28 April 2026.
Measurements for 38D
38D is built for an underbust ribcage measurement that falls in the 37–39 inch range, with a full-bust measurement around 43 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 — D — describes the difference between the two measurements; a D cup means the full bust is about four inches larger than the underbust — at this volume, unlined cups often give a more natural shape than heavily padded ones.
38D in Other Sizing Systems
EU, FR, and JP sizing read the band in centimetres, which is why 38D maps to 85D (EU), 100D (FR), and 85D (JP) — the same body, expressed in different units. AU sizing uses a small numeric scale (16D for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 38D reads as 38D on a UK label.
Sister Sizes for 38D
These sizes have the same cup volume as 38D. 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 38D 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 38D
D cups benefit from wider straps for comfort. Unlined or lightly-lined cups give a more natural shape at this size; very heavily padded cups can over-shape.
If your 38D 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 38D 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 38D is right for you.
38D — frequently asked questions
What measurements are a 38D bra?
A 38D bra fits an underbust (ribcage) measurement of roughly 37 to 39 inches (94–99 cm) and a full-bust measurement of about 43 inches (109 cm). The cup letter D reflects the difference between those two numbers.
What are the sister sizes of 38D?
The sister sizes of 38D are 36DD and 40C. They share the same cup volume as 38D but use a different band — go to 36DD for a tighter band, or up for a looser one. Try a sister size when the cup of your 38D fits but the band feels too loose or too tight.
What is 38D in UK, EU, and other sizing systems?
38D (US) converts to 38D in UK sizing, 85D in EU sizing, 100D in French sizing, 16D in Australian sizing, and 85D in Japanese sizing. The body is the same; only the labelling system changes.
Is 38D a small or large bra size?
In terms of how common it is, this size pairs an above-average band with a mid-range 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 middle end.
Not sure about your size? Measure yourself and double-check.
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