40F Bra Size

Measurements for 40F

40F is built for an underbust ribcage measurement that falls in the 39–41 inch range, with a full-bust measurement around 47 inches. The band number — 40 — is a larger band where reinforced construction starts to matter for long-day comfort. The cup letter — F — describes the difference between the two measurements; an F cup in UK and EU-style sizing corresponds to about six inches of difference between full bust and underbust — this is where mainstream lingerie sizing tends to thin out and specialist fuller-bust ranges take over.

40F in Other Sizing Systems

EU and FR sizing read the band in centimetres, which is why 40F maps to 90F and 105F respectively — the same body, expressed in different units. AU sizing uses a small numeric scale (18E for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 40F reads as 40E on a UK label.

The label "40F" follows the UK and broadly-European convention, where the cup letters go AA, A, B, C, D, DD, E, F. The same cup volume in US sizing is usually written as DDD (or DDD/F on labels that cross-reference both systems). If a US chart returns "40DDD" for your measurements, that is the same physical cup as 40F in UK/EU notation.

Sister Sizes for 40F

These sizes have the same cup volume as 40F. 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 40F 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 40F

F cups in UK sizing line up with US DDD/F. Three-part cups, side support panels, and full-coverage shapes typically fit more cleanly than thin moulded cups at this size.

If your 40F 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 40F 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.