Start with your regular garment size, then measure your bust, waist, hips, and torso with a fabric tape and compare each measurement to the specific brand’s size chart, choosing the smaller size when between two.
One wrong measurement sends you back to the returns counter. A swimsuit that rides up, gaps at the chest, or digs into your shoulders isn’t just uncomfortable — it kills your confidence in the water. The fix is not complicated: four measurements, one brand chart, and a single rule about stretch. Here is the exact process.
Why Your Regular Size Is Only The Starting Point
A swimsuit’s stretch fabric makes it look half its actual size on a hanger, so judging by appearance is the fastest route to a wrong fit. Your everyday dress size gives a useful starting bracket, but swimwear sizing varies dramatically between brands. A size 8 in Roxy may fit differently than a size 8 in TYR because each brand designs for a different body shape and activity level.
This is why the measurement step is not optional. You need a fabric tape measure and about three minutes.
The Four Critical Measurements And How To Take Them
Grab a soft fabric tape measure and stand in front of a mirror. Wear nothing over the area you are measuring, or wear the undergarments you plan to wear under the suit.
Bust
Run the tape around the fullest part of your chest, keeping it parallel to the floor. The tape should sit snugly without compressing the skin. Record the number, then measure your underbust — directly below the bust — separately if you are buying an underwire top.
Waist
Bend to one side to find the natural crease where your waist folds. That is the narrowest point. Wrap the tape around that spot. Do not suck in or hold your breath.
Hips
Stand with your heels together and measure around the widest part of your hips, usually about 7 to 9 inches below your waist. Stop the tape just before the thigh begins to narrow.
Torso Length
This is the one that trips up one-piece buyers. Start the tape at the center of your shoulder, bring it down across the fullest part of the bust, between your legs, and back up to the same shoulder point. The total length tells you whether a one-piece will fit your trunk without riding up or sagging.
Reading A Size Chart The Right Way
Once you have your four numbers, open the size chart for the specific brand you are buying. Compare each measurement to the chart’s ranges. The key rule: if your numbers fall into two different sizes, order the smaller one. Swimsuits stretch when wet, so a snug fit dry becomes a secure fit in the water. But if the suit leaves red marks or feels uncomfortably tight before it gets wet, it is too small — size up.
Anne Cole’s guide makes this clear: their XS fits a 33.5-inch bust and 25.5-inch waist, while their small bumps to a 35.5-inch bust and 27-inch waist. A half-inch difference can change the entire fit.
Brand Size Charts At A Glance
The table below shows how the same size label can mean different measurements across popular brands.
| Brand | Size | Bust (inches) | Waist (inches) | Hips (inches) |
|---|---|---|---|---|
| ROXY | XS | 32–33 | 24–26 | 35–36 |
| ROXY | XL | 39–40 | 31–34 | 41–43 |
| Anne Cole | XS/4 | 33.5 | 25.5 | 36.5 |
| Anne Cole | XL/16 | 41 | 33 | 44 |
| TYR Sport | 6 | 33–34 | 27–28 | — |
| TYR Sport | 14–16 | 39–40 | 34–35 | — |
| ASOS | XS | 31 | 23.75 | — |
| ASOS | XL | 45.5 | 38.5 | — |
Notice that ASOS’s XL bust measurement (45.5 inches) is larger than ROXY’s XL (39–40 inches). That gap shows why you must check every brand individually rather than assuming your size carries over.
How To Fit Specific Body Shapes And Needs
Your body shape determines which measurement matters most. For hourglass figures with a larger rear, prioritize the hip measurement and let the top fit follow — a bottom that fits correctly may make the top feel snug, but the reverse choice leaves you pulling the suit down all day. If you carry more weight in your bust, buy for the bust measurement and accept that the waist and hips may need alteration or a different style.
Plus-size swimwear options with fuller coverage often use a separate sizing system, so check whether the brand offers Misses, Plus, or Cup size charts separately — Miraclesuit, for example, provides DD to DDD cup options alongside standard misses sizing.
Tops, Bottoms, And One-Pieces: Different Rules For Each
The fit strategy shifts depending on the swimsuit style you are choosing.
Separate Tops
For bikini tops, the bust measurement is the primary anchor, but the band fit underneath matters just as much — you should be able to slide two fingers under the band without lifting it away from the ribs. Underwire tops also require an accurate underbust measurement, not just the full bust number. If you are between cup sizes, choose the larger cup and adjust the band tightness.
Separate Bottoms
The hip measurement leads here. Bottoms should sit flat at the hip bone without rolling or digging in. For high-waisted styles, the waist measurement also becomes critical since the waistband needs to stay put without rolling down.
One-Pieces
Torso length is the deciding factor for one-pieces. If your torso measurement is longer than the brand’s range for your size, the suit will ride up at the crotch and create a gap at the back. Monday Swimwear includes a dedicated torso measurement on its fit guide precisely because this is the most commonly missed dimension. If the brand does not list torso length, compare the suit’s center-front and center-back seam measurements to your own.
Common Fit Problems And What They Mean
| Fit Issue | Likely Cause | What To Do |
|---|---|---|
| Straps dig into shoulders | Bust too large for the top size, or torso too long for a one-piece | Size up in the top or check torso length |
| Suit rides up at crotch | Torso too long for the one-piece size | Look for “long torso” styles or size up |
| Gaping at the chest | Bust smaller than the top’s design range | Size down or try a padded or ruched top |
| Red marks after wearing | Suit is too small | Size up — stretch when wet will not fix this |
One overlooked issue: judging a swimsuit’s size by its look on the hanger. Because swimsuit fabric stretches significantly, the garment looks much smaller than its actual fit size. This visual trick causes many people to buy a size too large. Trust the numbers, not the hanger.
Which Sizing Strategy Works For Your Body Type
The most reliable approach is ordering two sizes — your calculated size and one size up — if the brand offers free returns. Knix explicitly recommends this method. Try both on at home with the tags still attached and return the one that fits worse. For competitive or training suits, TYR recommends sticking close to your measured size since the compressed fabric is designed for hydrodynamic performance rather than lounge comfort.
FAQs
FAQs
Should I size up or down if I am between swimsuit sizes?
Size down. Swimsuits are made from stretch fabric that expands when wet, so the smaller size will fit securely once you are in the water as long as it is not causing red marks or discomfort before getting wet.
Does torso length really matter for a one-piece swimsuit?
Yes — this is the most common sizing mistake. If your torso is longer than the suit is designed for, the suit will ride up at the crotch and sag at the back, regardless of your bust or waist measurements.
Why does my swimsuit size differ between brands?
Each brand uses its own fit model and design target. A TYR training suit is cut snug for performance, while a ROXY or ASOS swimsuit allows more room for casual wear. Always check the specific brand’s size chart.
Can I use my dress size to pick a swimsuit?
Only as a starting point. Your dress size gives you a rough bracket, but because swimsuit fabric stretches and brand charts vary, you must measure your bust, waist, hips, and torso to confirm the right fit.
How tight should a swimsuit feel when dry?
Snug but not painful. You should not see red marks, feel compression that makes breathing uncomfortable, or struggle to get the suit on or off. A suit that is too tight when dry will not become comfortable when wet.
References & Sources
- Knix. “What Size Swimsuit Should I Buy?” Covers measurement steps, torso importance, and the between-sizes rule.
- ROXY. “Women’s Swimwear Size Chart.” Provides XS–XXL inch measurements for bust, waist, and hips.
- Anne Cole. “Size Guide.” Details inclusive sizing from XS/4 to 5X/24W with torso lengths.
- TYR Sport. “Sizing – Swim.” Lists numerical adult sizing for competitive and training suits.
- Monday Swimwear. “Fit Guide.” Includes cup sizing A–G and torso measurements for one-pieces.