Size 40O Swimwear
Also labeled UK 40K and EU 90O
A 40O bust needs swimwear that fits like a good bra, not a dress size. Look for a level band, cups that cover you at the sides, and straps that only steady the fit. Use the Swimwear Size Chart to match US, UK and EU labels.
Checking the Band on a 40O Swimsuit
A 40 band has to hold its place across a wide back, and a band that is too loose will slide up as soon as you move. If the suit feels snug at the ribs but loose under the arms, check the side panels before changing the band size. Fasten the band, lift both arms over your head, and check that the back has not moved.
Wear the suit for ten minutes before you judge it, then check that a large band still sits level. Swim fabric settles as it warms to your body, and a band that loosens then will loosen more in the water.
Cup Coverage for a 40O Bust
An O cup often needs a wider cup base as well as more depth, so check where the cup meets your side. Very deep cups put more weight on the straps, so the band needs to carry its share for the straps to feel comfortable. Lean forward, settle each side into its cup, then stand and check the edges.
In UK sizing, look for 40K. A UK K is a US O, which is four cups larger than a US K.
When 40O Swim Straps Dig In
Straps should steady the suit, not hold it up. If they leave marks on your shoulders, loosen them and see whether the band and cups stay in place on their own. With a large band, a band that has loosened in the water is the most common reason straps start to dig.
Shopping for everyday wear too? Browse our 40O bras.
Frequently Asked Questions About Size 40O Swimwear
How does 40O swimwear convert to UK and EU sizes?
US 40O is labeled UK 40K and EU 90O, and that UK K is four cups larger than a US K. Follow the system printed on each label.
Should 40O swimwear fit more snugly than my bra?
Yes, a little, especially in the band. Many swim fabrics give once wet, so a large band that feels firm when dry usually sits right in the water. It should still let you breathe deeply without pinching.
Can I wear my usual 40O bra size in swimwear?
Yes, your 40O bra size is the right place to start for swimwear sized by band and cup. Swim cuts vary, so with an O cup check the band and cup edges in each suit rather than trusting the label alone.
Why does my 40O swimsuit band ride up in the water?
Most often, the band has loosened once wet and is no longer anchoring an O cup. Refasten it more firmly and check the fit again after a few minutes in the water. Tighter straps tend to make it worse.
How do I know if a 40O one-piece is too short in the torso?
The straps dig into your shoulders, the leg openings pull up, and the suit feels like it is dragging down. With an O cup, the bust uses extra length, so check the torso fit while sitting as well as standing.
Is a tankini a good option for a 40O bust?
Yes, a tankini can help when one-piece torso length is the problem, because the top and bottom are separate. The top still needs cups deep enough for 40O and a band that stays firm, which matters even more on a large band.