Swimsuit Size Converter
Find your swimsuit size in US, UK, EU, and AU — for one-piece, bikini tops, and bikini bottoms.
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How to measure for a swimsuit
Swimsuit sizing trips up more people than any other category — partly because brands disagree, partly because swimsuits stretch in water and tighten when wet. The fix: measure, don't guess.
1. Bust (for one-pieces and bikini tops)
Wrap a soft tape measure around the fullest part of your bust. Don't pull tight.
2. Underbust / band
Measure tightly around the rib cage, directly under your bust. This is your band size.
3. Waist
Measure at the narrowest point — usually 2 inches above your belly button.
4. Hips (for bottoms)
Measure around the fullest part of your hips. Stand with feet together.
5. Torso (one-piece only)
Measure over your shoulder, down between your legs, and back up to the same shoulder. This is the most-skipped step and the #1 cause of "the suit fits everywhere except it's pulling".
Brand notes — which swimsuit brands run small or large?
Runs small (size up 1)
Triangl, Frankies Bikinis, Aerie — designed for a snug fit. Size up if you're between or want comfort.
True to size
Speedo, TYR, Athleta, Lululemon, Patagonia, Old Navy — reliable sizing, usually 1:1 with your apparel size.
Runs large / loose
Andie, Summersalt, Eberjey — generous, flattering cuts. Size down if you want a snug athletic fit.
Special note: Brazilian bikinis
Brazilian-cut bottoms are intentionally smaller than US/EU equivalents — they show more skin. If you're not used to them, size up at least 1, sometimes 2.
Frequently asked questions
What is a US small in EU swimsuit sizing?
US small = EU 36 = UK 8 = AU 8 for most one-piece and bikini brands.
Should I size up for swimsuits?
Sometimes. Most US brands run true to size if you go by your apparel size. European and South American (Brazilian) brands tend to run smaller — size up 1 to be safe. Triangl is famous for running small.
How do I size a bikini top with cups?
Bikini tops with cup sizing (e.g., 32B, 34C) fit much better than S/M/L. Use your regular bra band + cup size. If you're between bands, the snugger one is usually better — swim fabric stretches in water.
What if my top and bottom are different sizes?
Buy them separately. Most brands sell mix-and-match bikinis specifically for this reason — there's no rule that says they have to match. Andie, Summersalt, Aerie, and Old Navy all allow it.
Do swimsuits stretch?
Most stretch slightly when wet (1–2%) and recover when dry. Don't size up expecting a "stretch in" — buy your true size. If anything, suits get LOOSER over a season with sun + chlorine wear.
What about plus-size swimwear?
Plus-size swim is sized the same way (number-based, not S-XL), but choices are best from Lands' End, Swimsuits For All, Torrid, Eloquii, ASOS Curve, Aerie. Avoid Triangl, Frankies — limited size range.