Size Guide

size chart

Size		Bust
XXS	00	30.5 - 32
XS	0	32 - 33.5
S	2-4	33.5 - 35
M	6-8	35 - 37
L	10-12	37 - 39
XL	14-16	39 - 41.5
2XL	18-20	41.5 - 44
3XL	22-24	44 - 47

Size		Waist	Hips
XXS	00	23 - 24.5	33 - 34.5
XS	0	24.5 - 26	34.5 - 36
S	2-4	26 - 27.5	36 - 37.5
M	6-8	27.5 - 29.5	37.5 - 39.5
L	10-12	29.5 - 31.5	39.5 - 41.5
XL	14-16	31.5 - 34.5	41.5 - 44
2XL	18-20	34.5 - 37.5	44 - 47
3XL	22-24	37.5 - 41	47 - 50.5

Size		Bust	Waist	Hips
XXS	00	30.5 - 32	23 - 24.5	33 - 34.5
XS	0	32 - 33.5	24.5 - 26	34.5 - 36
S	2-4	33.5 - 35	26 - 27.5	36 - 37.5
M	6-8	35 - 37	27.5 - 29.5	37.5 - 39.5
L	10-12	37 - 39	29.5 - 31.5	39.5 - 41.5
XL	14-16	39 - 41.5	31.5 - 34.5	41.5 - 44
2XL	18-20	41.5 - 44	34.5 - 37.5	44 - 47
3XL	22-24	44 - 47	37.5 - 41	47 - 50.5

onewith size quiz

everyone’s unique, and no quiz can capture every preference or body type — but this is the next best thing to trying on in person.

disclaimer: results are a guide, not a guarantee. fit preferences may vary.

Three women in swimsuits smiling and holding hands on a beach, showing diverse body types.

See Every Size, On Every Body

Swimsuit shopping online can never be the same as trying on in-store. Though, TBH, we actually prefer trying on swim in the comfort of our own home (we digress.)

We get how tricky online swim shopping can be. Human bodies are more dynamic than just a simple little size chart. That is why we highly recommend…no, we insist…that you take our size quiz! Take the quiz once, and your best size for each and every style on our site appears on the product page itself. Also, don’t forget to check out our “See It On” section, where you can get a glimpse of how our swim fits IRL, on bodies from XXS–3XL.

The goal? Less guessing, less over-ordering, and way more confidence at checkout. No more ordering two sizes just to return one, which, honestly, can be really tough on a small business. And, importantly, no more spiraling over which size to pick.

Just find your best fit, place your order, and get ready to feel amazing in your swim that doesn’t dig in.

1 FREE exchange on eligible US orders

size inclusive (XXS-3XL)

patented, US Patent No. 12,357,039

See it in your size

Angled view of Foxon bandeau bikini top on model showing front tie, wide straps and seamless fit, seated on rocks by the ocean — andrypena / XXS + XXS

Woman in a red onewith one piece swimsuit standing on a boat with blue water in the background — kareenasinghh / XS

Woman standing on a rocky shoreline wearing a bright blue bikini, hands behind her head — kareenasinghh / XS + XS

Woman in a red onewith one piece swimsuit standing on a boardwalk with greenery in the background — carolyn.mhickman / S

Woman wearing a blue onewith bikini standing against a wooden wall. — dayj.doll / S + S

Woman wearing a blue onewith bikini top in a pool — megdlyn / S

Woman in a blue onewith bikini and sunglasses standing on a balcony with a view of a marina — ivana_ferro / S + M

Woman in a black onewith bikini standing on a beach — alyssa.models / S + M

onewith founder Hayley wearing a onewith black one piece swimsuit taking a mirror selfie — onewithswim / S

Woman in black one-piece swimsuit standing on a muddy beach with hands on hips, wooden pilings and shallow water behind her. — ahmeimae / S

Back view of onewith Idlewild High-Neck One Piece in black showcasing low scoop back and high-cut leg with ocean background — ahmeimae / S

Woman wearing a black bikini on a beach — alexhakim16 / S + M

Woman in a black onewith bikini standing on a beach with water and sky in the background — ahmeimae / S + M

Woman wearing a brown onewith bikini with a bag — onewithswim / S + S

Woman in a onewith bikini and hat on a beach at sunset — carolyn.mhickman / S + S

Woman in a black onewith bikini and hat standing in the ocean — emily_shultis / S

Three-quarter view of black Westerly bikini top and high-waisted bottoms showcasing a center front tie on a model at a pool — traceydoes_ / S + M

Woman wearing a blue onewith bikini taking a mirror selfie — onewithswim / S + S

Woman wearing a black onewith bikini taking a selfie — lordnavji / M + M

Woman in a blue onewith bikini standing on a dock by water — ahmeimae / M + M

Three-quarter view of Hampton bottom in black on a model showcasing high-rise, full-coverage fit with raw-cut edges at poolside — traceydoes_ / S + M

Smiling woman kneeling on wet sandy beach, wearing a black bikini, hands in her hair — anaidalyramos / M + M

Woman in a black onewith bikini standing against a teal door. — Anaidayl / M + M

Reclining woman wearing a black bikini top on wet rocks, showing necklaces and a ring — ahmeimae / M

Woman in a blue onewith bikini and pink hat by a pool — ivana_ferro / S + M

Woman in a black onewith bikini sitting on a beach with ocean in the background — alyssa.models / S + M

Woman in a black onewith bikini sitting on a counter — anaidalyramos / M + M

Woman in a black onewith bikini on a boat — ivana_ferro / S + M

Woman in a red onewith one piece swimsuit standing by the ocean — ashleyyharveyy / L

Woman sitting on a dock by a body of water wearing sunglasses and a black onewith bikini top. — ceciliakauffmanharris / L

Woman wearing a black onewith bikini standing on a beach — chloewoz / XL

Woman in a blue onewith bikini standing in a pool with a flower in her hair — summerleilani_ / XL

Woman wearing a black onewith bikini standing on a balcony. — chloewoz / XL + XL

Plus-size woman in a black bikini leaning on a white porch railing, smiling at the camera — chloewoz / XL + XL

Woman wearing a black onewith bikini standing on a balcony overlooking a beach with palm trees. — wendyfrita / 2XL + XL

Woman wearing a black onewith one piece swimsuit in a pool — gracedotymusic / 2XL

Woman in a blue onewith bikini holding a drink under a palm tree — cheyenneolson / 2XL

Mirror selfie of Idlewild High-Neck One Piece in Abyss black on model showcasing high neckline and full-coverage fit — gracedotymusic / 2XL

Woman wearing a black onewith bikini sitting on a stool indoors. — gracedotymusic / 2XL + 2XL

Woman in a blue onewith bikini standing on a boat with rocky cliffs and blue water in the background — Marisa / 2XL + 2XL

Woman in a black onewith bikini standing on a rocky beach with houses and trees in the background. — tatumblinncoffey / 3XL + 3XL

Plus-size model wearing a red beyond-seamless one-piece swimsuit on a sunny tropical shoreline with palm trees — hayleyhermsofficial / 3XL

Woman in a black onewith bikini standing on a sandy beach with water and boats in the background. — ariellamayamendes / 2XL + 3XL

Front view of onewith blue swim bottom on model showing smoother, more secure fit compared with black swim bottom

important info for when you get your onewith

how to warm up your onewith

this is swimwear unlike anything else on the market, so with that, it has some special instructions to truly get a fit that's onewith your body ✨ 'warming up your onewith’ (aka giving the garment a stretch) is MISSION-CRITICAL to the fits-like-undies vibe. your swim actually SHOULD dig in a bit to start if it’s your proper size. then, with a stretch at the openings, it should fit and feel smooth, like a second skin (and/or your fave seamless undies) 🫧

what to know about sizing

can I just order a few sizes and styles and return what doesn't fit?

⛔ bracketing + high-quantity first orders are discouraged: while we understand the desire to find your best size and style, ordering multiple variants with the intention of returning what doesn't work creates inventory challenges for us as a small business and compromises hygiene best practices. we encourage conscious consumerism — start small and mindful, and once you've found your perfect fit, stock up! please note that returns of 4 or more items are subject to an additional processing fee.