30C Bra Size

Measurements for 30C

30C is built for an underbust ribcage measurement that falls in the 29–31 inch range, with a full-bust measurement around 34 inches. The band number — 30 — is a smaller band that needs to sit firmly without cutting in. The cup letter — C — describes the difference between the two measurements; a C cup means the full bust is about three inches larger than the underbust — this is the threshold where cup shape (full-cup, demi, balconette, plunge) starts to make a noticeable difference.

30C in Other Sizing Systems

EU and FR sizing read the band in centimetres, which is why 30C maps to 65C and 80C respectively — the same body, expressed in different units. AU sizing uses a small numeric scale (8C for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 30C reads as 30C on a UK label.

Sister Sizes for 30C

These sizes have the same cup volume as 30C. 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 30C 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 30C

C cups work well across most bra styles. If you spill over in one brand but fit fine in another, cup shape and depth vary by maker — the size on the label is only part of the story.

If your 30C 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 30C is close but not quite right, these neighbouring sizes are the most useful next places to look:

Not sure about your size? Measure yourself and double-check.