What Size Bikini Am I? A Real Two-Piece Sizing Guide
What Size Bikini Am I? A Real Two-Piece Sizing Guide
By the Bikini Uni team. Updated May 2026.
Why your bikini top and bottom should probably be different sizes, and how to actually know what to order.
The fundamental sizing problem
Most bikinis are sold as a matching set in a single size. You order a "medium," you get a medium top and a medium bottom.
The problem: almost no woman is the same size on top and bottom. You might be a 32 on top and a 36 on the bottom. You might be the reverse. Forcing both halves to share a number guarantees one won't fit.
This is why most women's first bikini disappointment is the same — the top fits, the bottom is loose. Or the bottom fits, the top is too tight. The suit isn't wrong; the matching-size system is wrong.
Two solutions exist. Buy bikinis with independent top and bottom sizing, ordering each half separately. Or buy the size that fits the half you care more about and adjust the other half.
How to actually measure yourself for a bikini
You need three measurements. Use a soft tape, against the skin or light underwear, with the tape laid flat — not pulled tight, not loose.
Bust. Measure around the fullest part, with the tape parallel to the floor. Determines bikini top size and most one-piece sizes.
Underbust (optional). Measure directly under the bust, where a bra band sits. Useful context but not the sizing number for swim.
Waist. Measure the narrowest part of your torso, about an inch above the navel. This is your true waist — not your jeans waist (which is usually lower).
Hips. Measure the fullest part of your hips and rear, tape parallel to the floor, feet together. Determines bikini bottom size.
Write the numbers down. Don't trust your memory between measuring and shopping.
How swim sizing works (the 28-40 system)
Most athletic and competition swimwear uses numerical sizing rather than S/M/L. The numbers correspond roughly to body measurements in inches.
Women's tops and one-pieces: the size number is generally aligned with the bust measurement. A 32-inch bust typically fits a size 32 suit. A 33-inch bust may want a 34 for ease or 32 for snugness.
Women's bottoms: the size number tracks the hip measurement. A 38-inch hip generally fits a size 38 bottom.
Men's jammers, trunks, and diver-cuts: the size number is the waist in inches. A 32-inch waist is a size 32 jammer. Most men size down 1-2 inches from their pants size because pants sit lower than the true waist.
Always check the brand's specific size chart — sizing varies between makers. A 32 in one brand can be a 34 in another. The Bikini Uni size chart is on every product page.
Bra size ≠ bikini size: the conversion problem
Your bra size and your bikini top size measure different things. A bra band (the "34" in 34B) measures your underbust. A bikini top size measures your bust.
A 34-inch underbust corresponds to roughly a 35-inch bust, so ordering a "size 34" bikini against a 34-band bra runs about three inches small.
| Your bra size | Approximate swim top size |
|---|---|
| 30A / 32A / 32B | 28 to 30 |
| 32B / 34A / 34B | 30 to 32 |
| 34B / 34C / 36A / 36B | 32 to 34 |
| 34C / 34D / 36B / 36C | 34 to 36 |
| 36C / 36D / 38B / 38C | 36 to 38 |
| 38C / 38D / 40B / 40C | 38 to 40 |
Full breakdown of the conversion logic in our bikini top sizing 101 post.
The four fit tests every bikini should pass
Try the suit on dry first, then wet (a sink rinse works). Run through these:
- Pinch test (top). Pinch the fabric at the side of the cup. Pull more than half an inch from body = too big. Can't pull any = too small.
- Two-finger test (bottom). Slide two fingers under the waistband at your hip. Two fits easily = right. One barely fits = too tight. Three or more = too loose.
- Walk test. Walk, sit, stand, bend to pick something up. If anything shifts or you have to adjust, the fit isn't right.
- Wet test. Wet the suit, repeat tests 1-3. Swimwear stretches when wet — a perfect dry fit can be loose wet, so a slightly snug dry fit is usually correct.
"If you have to adjust your bikini three times across one beach day, the sizing is the problem, not your body."
How to fix a bikini bottom that's too big
Already bought a bikini with a loose bottom? Four options before tossing it:
1. Tumble dry low (synthetic suits only). Goes against our care guide, but one low-heat cycle can shrink a polyester/nylon-blend bottom by half a size. Shortens the suit's life. If you're going to toss it anyway, worth trying.
2. Sew in an elastic band. Open the inside of the waistband, insert swim-grade elastic, sew the casing back closed. Adds genuine grip. Basic sewing skills, 30 minutes.
3. Add side ties. Sew two short fabric strips, one each side of the waistband. Knot to draw the bottom in. Less invasive than the elastic option.
4. Take it to a tailor. A tailor working with stretch fabrics can resize bikini bottoms for $15-30. Cheaper than buying new. Fit will be permanent.
How to know if a bikini top is too small
Signs you've sized down too far:
- Straps dig red lines into your shoulders within an hour
- Cups don't fully cover — skin spilling at the top or sides
- Band rides up your back instead of sitting horizontal
- You can feel underwire (if any) pressing into your ribcage
- You have trouble taking a deep breath
Any single sign = size up. Don't power through; the top won't stretch into a comfortable fit.
Sizing specialty cuts (cinched-waist, one-shoulder, high-leg)
The general numerical sizing applies to most styles, but a few cuts work differently:
Cinched-waist bottoms have built-in adjustability. Size to your hips, then tune the cinch. If between sizes at the hip, size up — you can cinch tighter, but can't add fabric. Full breakdown in our cinched-waist bikini guide.
One-shoulder one-pieces use letter sizing (XS-XL) because the asymmetric cut sizes by overall body proportion. Between sizes? Size down. More in our one-shoulder swimsuit guide.
High-leg cuts sit higher on the hip. The two-finger test applies at the leg opening as well as the waist.
Frequently asked questions
How do I figure out my bikini size?
Measure bust (fullest point), waist (narrowest point above navel), and hips (fullest point, feet together) with a soft tape parallel to the floor. On numerical swim sizing, the size number roughly matches your measurement in inches.
Should I size up or size down if I'm between bikini sizes?
Size down on training/athletic suits — the fabric loosens with wear. Size up on leisure suits if comfort matters more than fit precision. For cinched-waist bottoms, size to your hips and use the cinch.
Can I order different sizes for the top and bottom of a bikini?
Yes, if the brand offers it. Most Bikini Uni two-pieces are sold with independent top and bottom sizing — select each half separately at checkout.
What's the difference between bra size and bikini size?
Bra band size measures your underbust; bikini top size measures your bust. A 34-band bra has roughly a 35-inch bust, so a "size 34" bikini ordered against a 34-band bra runs ~3 inches small.
How do I fix a bikini bottom that's too loose?
Options: take it to a tailor specializing in stretch fabrics ($15-30), sew in a swim-grade elastic band, add side ties, or do one low-heat dryer cycle to shrink synthetic fibers slightly (shortens suit lifespan).
Do swim sizes change as my body changes?
Yes. Re-measure every season. Old swimsuits stretch out, so referencing an old suit is unreliable.
What if my measurements fall between two sizes on the chart?
Message us with your bust, waist, and hip numbers before ordering. We'll recommend the size we'd ship to a friend with the same measurements. Free, almost always faster than returning.
Find your fit
Most Bikini Uni two-pieces are sold with independent top and bottom sizing. Sizes 28-40 across the women's mainline including the Bella Cintura, La Sirenita, Ameri-Cali, and Dos Tierras sets. All sewn by hand in Cali, Colombia.
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