Swimwear Fit Guide: Measure and Choose the Right Suit

Good swimwear should stay in place when you walk, sit, bend and get in and out of water, without digging in or leaving gaps. That is a fit problem, not a body problem, and it is solvable with the right measurements and a few checks. This swimwear fit guide shows you how to measure, how each part of a suit should sit, how to choose cuts for the way you actually use them, and what to look for when you are ordering online and cannot try anything on first.

Start with the right measurements

Use a soft tape measure, keep it level and snug but not tight, and measure over bare skin or a thin layer:

• Bust: around the fullest part of the chest.
• Underbust: directly under the bust, where a band would sit. This governs the fit of structured tops.
• Waist: at the narrowest point, usually just above the navel.
• Hips: around the widest part of the hips and seat.
• Torso length (for one-pieces): start at the top of one shoulder, run the tape down the front of the body, through the legs and back up to the same shoulder. This single number decides whether a one-piece feels comfortable or pulls on the straps and crotch.

Compare your numbers with the brand’s chart, using our guide to reading clothing size charts if you are unsure of the difference between body and garment measurements. Many swim brands size tops and bottoms separately, so buying a different size for each is normal, not a failure.

How each part of the suit should fit

Bikini and swim tops

• The band or underwire: it should feel snug and stay level around your back. If it rides up when you raise your arms, it is too big.
• The cups: they should cover your breast tissue fully with no spilling over the top or sides and no empty wrinkles.
• The straps: they should lie flat without cutting into the shoulders. If they slip, tighten them or choose a style that ties or crosses at the back.
• Triangle tops: the string ties provide adjustability but not support. For larger busts or active swimming, choose wider straps, an underwire or a bandeau with a supportive band.

Swim bottoms

• Leg openings: they should sit flat against the skin with no folds and no pinching. A thin line of elastic shows you the fit is right; a deep groove shows it is too small.
• The waistband: it should not roll down or dig in. High-waisted styles should stop at or just above the navel without bunching.
• Coverage: full-coverage, classic, cheeky and high-leg cuts each show a different amount of seat. Choose the coverage you will feel comfortable in while moving, because a suit you are constantly adjusting is not a comfortable suit.

One-piece swimsuits

• Torso length: when standing, straps should sit without tension and the crotch panel should sit flat, not pulled up. Pulling means the torso is too short for you.
• The bust and side seams: look for smooth seams with no puckering at the ribs.
• Back coverage: low-back designs may need a specific bra or a stick-on solution, so check what the product page describes.

Swimwear silhouettes and what they are good at

• High-waisted bottoms: they add coverage at the tummy and hips and pair well with cropped tops. They may ride up on a short torso.
• Classic or mid-rise bottoms: the most versatile all-rounders for swimming and lounging.
• Skirted bottoms and swim shorts: they add coverage at the upper thigh and feel comfortable for chasing children or beach games.
• Tankinis: a two-piece with a longer top. The advantage is being able to size the top and the bottom separately while still keeping a covered midriff.
• Wrap, ruched and gathered one-pieces: the fabric texture hides small creases and offers some tolerance if your size fluctuates.
• Bandeau and strapless styles: stylish but reliant on the band’s grip. They suit sunbathing more than swimming laps.

Whichever you choose, stay with the style you feel most at ease in. There is no “correct” swimsuit for any body type; the best suit is the one you forget you are wearing.

Match the suit to the activity

Ask how you will use the suit before you choose it. For lounging and sightseeing, almost any cut works. For lap swimming or water sports, choose secure fabric, wider straps and a snug fit, and avoid loose ties that undo in water. For traveling with children, pick opaque fabric and a cut you can bend and run in. For holiday sunbathing, consider a style with little strapping if you want fewer tan lines, and remember that pale colors and thin fabric may become more see-through when wet. Our guide to beach cover-up outfits also shows how to transition between the pool and lunch.

Fabric, lining and stretch

Swim fabrics are usually blends of a stretch fiber such as elastane with nylon or polyester. The higher the stretch content, the more forgiving the suit will be, but the stretch also wears out with chlorine, sunscreen and heat. Look for a lining in the front, or full lining in pale colors. Remember that suits often feel snug when dry and loosen slightly after time in the water, so a suit that feels comfortably firm rather than tight is usually right. If the product page lists fabric composition and lining details, use them; if not, choose based on the size chart and treat your first swim as a test.

Sizing in-between: which way to go?

If your bust and hips fall in different sizes, buy separate sizes for top and bottom wherever separates are sold. If you fall between two sizes on the same piece, size up when the suit has a lot of structure, an underwire or a fixed back, and size down when the fabric is soft, stretchy and has adjustable ties. If you are between sizes because of a long torso, look for a longer-torso or a two-piece style rather than forcing a standard one-piece.

Buying swimwear online without a fitting room

1. Measure yourself the day you order, not from memory.
2. Read the size chart and note whether the numbers are body measurements or garment measurements.
3. Choose a size for your largest measurement in that area rather than the smallest.
4. When the suit arrives, try it on with the tags still attached, walk, sit and raise your arms. Do not wear it in the water until you are sure the size is right.
5. Check delivery and return details on the shipping and returns page before you order.

For the wider approach to ordering online, see our guide to buying clothes online.

A one-minute fit test for any new suit

Once a suit arrives, run through this short routine in front of a mirror. Raise both arms overhead and check that the band or bodice stays put. Squat as if picking something up from the floor and see whether the bottoms slide or pinch. Lean forward and check that nothing spills out at the top or sides. Turn around and look at the back: the seam should sit flat and the straps should not twist. If the suit passes all four, you can be confident it will manage everyday movement, and if it fails only one, an adjustable strap or a size change on that piece alone is often enough.

Caring for swimwear so the fit lasts

Rinse the suit in cool, clean water after every wear, especially after chlorine or salt. Hand wash with mild soap, do not wring it out, and squeeze out water gently in a towel. Dry it flat in the shade, since direct sun and dryers weaken elastane. Avoid sitting on rough surfaces such as concrete pool edges, which can snag delicate fabric.

FAQ: Swimwear fit

How tight should a swimsuit be?

Firm and supportive without leaving deep marks or restricting your breathing. You should be able to move freely, and the suit should stay put when you jump or bend.

Why does my swimsuit top gape or slip?

Most often the band is too large or the cups are the wrong shape for your bust. Try a smaller band size with a larger cup, or a style with an adjustable back and wider straps.

What is the best swimsuit for a long torso?

A two-piece or tankini avoids the tension of a standard one-piece, and some styles come in long-torso lengths. Measure your torso length and compare it with the chart.

Should I size up in swimwear?

Not automatically. Follow your measurements first, then size up only if you fall between two sizes on a structured piece, or size down on soft, stretchy pieces.

Find your next suit in the ADDMPS swimwear collection, and check each product page for sizing and fabric details.

Edited by the ADDMPS Style Team.