Size 40N Swimwear
Also labeled UK 40JJ and EU 90N
Swimwear sized as 40N follows your bra size, with the band and cup working together. On a large band, wet fabric can loosen quickly, so a firm band matters as much as cup depth. Check conversions in our Swimwear Size Chart before you choose.
Keeping the 40N Band Level in Water
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. Look for a band area that sits flat without rolling, since a narrow band can twist on a larger frame. Once the band feels right, the cups and straps are much easier to judge.
Notice where the suit feels tight first. On a large band, pressure at the ribs points to the band, while pressure on the shoulders usually means the torso or straps need attention.
How 40N Swim Cups Should Hold You
An N cup is a very deep cup, so it needs coverage that reaches back toward the underarm and down to the band. With this much depth, small changes in cup shape can matter more than the letter, so compare how each cup holds you. In a one-piece, the cups should line up with your bust rather than sitting high or low.
UK tags call it 40JJ. UK sizing doubles the letter here, so a US N reads JJ.
Torso Length in a 40N One-Piece
A one-piece has to fit your bust, your torso and your hips at once. With a very deep cup, the cups take up more of the fabric's length, so a suit can feel short through the body even when the band is right. If the straps dig in and the leg openings pull up, look for a longer torso or try a tankini.
Want a matching everyday bra? Try our 40N bras.
Frequently Asked Questions About Size 40N Swimwear
Which UK label matches US 40N swimwear?
US 40N is labeled UK 40JJ and EU 90N, because UK sizing doubles the J for this cup. Read the size system on every tag.
How do I help 40N swimwear keep its fit?
Rinse the suit in cool fresh water after each swim and dry it flat in the shade. Fabric that keeps its shape keeps the band on a large band firm for longer.
Which works better for 40N, a one-piece or a tankini?
It depends on your torso more than your bust. A one-piece spreads support through the whole garment but needs the right body length, while a tankini top relies on its band and cups. With a very deep cup on a large band, choose whichever keeps the band level when you move.
Why do 40N swim cups wrinkle when the band fits?
Wrinkles with a good band usually point to cup shape, not size. With a very deep cup, settle your bust again, then compare a different cup shape or coverage before going down a cup.
Can a swimsuit give 40N the same support as a bra?
Yes, a suit sized by band and cup can come close, as long as the band is firm and the cups have enough depth for a very deep cup. A suit sized only by dress size usually cannot hold 40N the same way.
Does a 40N bust need more side coverage in swimwear?
Yes, usually. With a very deep cup, tissue can slip out near the underarm when you move, so look for cups that reach back toward your side.