38F Bra Size
38F 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.
38F 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 | 38DDD |
| One cup bigger | 38G |
| One cup smaller | 38DD |
| Approx. top size | L–XL · UK 14–16 / US 10–12 |
Measurements for 38F
38F 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 — F — describes the difference between the two measurements; a US F cup means the full bust is about seven inches larger than the underbust — it is the same cup as a US DDD (labels often read DDD/F) and a UK E. This is where mainstream lingerie sizing tends to thin out and specialist fuller-bust ranges take over.
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38F in Other Sizing Systems
EU, FR, and JP sizing read the band in centimetres, which is why 38F 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 38F reads as 38E on a UK label.
Is 38F the same as 38DDD? In US sizing, yes: US brands use DDD and F for the same cup (labels often read "DDD/F"), so 38F and 38DDD are the same size. In UK sizing this cup is called 38E. If your 38F came from a UK brand, it is one cup larger — a UK 38F matches a US 38G. 38F is not the same as 38DD, which is one cup smaller.
Sister Sizes for 38F
These sizes have the same cup volume as 38F. 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 38F 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 38F
A US F cup is the same volume as a US DDD (UK E). Three-part cups, side support panels, and full-coverage shapes typically fit more cleanly than thin moulded cups at this size.
If your 38F 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 38F 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 38F is right for you.
38F — frequently asked questions
What measurements are a 38F bra in inches and cm?
A 38F 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 F reflects the roughly 7-inch (18 cm) difference between those two numbers.
What size is equivalent to 38F? (sister sizes)
The sister sizes of 38F are 36G (tighter band, one cup letter up) and 40DD (looser band, one cup letter down). They hold the same cup volume as 38F on a different band. Try a sister size when the cups of your 38F fit but the band feels too loose or too tight.
What is 38F in UK, EU, and other sizing systems?
38F (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 38F 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 38F 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 38F 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 38F?
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 — 40F has more cup volume than 38F, not the same.
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