Swimsuit Sizing Guide: How To Measure for Bikinis and One-Pieces

The best way to choose the right swimsuit size is to measure your bust, waist, hips, and torso. Then compare those numbers to the brand’s swimsuit measurement chart. 

Key Takeaways

• Your bust, waist, hips, and torso length determine how a bikini or one-piece swimsuit will fit.
• Always check the swimsuit measurement chart instead of relying on your clothing size to guide you.
• A swimsuit should lie flat against your body, stay in place when you move, and not dig in, sag, or gap.

Shopping for swimwear online can be frustrating because brands use different sizing systems. A size marked “medium” might fit like a small in one label and like a large in another. To avoid buying multiple swimsuits and returning them, you’ll need accurate measurements and a basic understanding of swimsuit sizing. 

This guide explains how women’s swimsuit sizes work, how to measure yourself properly for both bikinis and one‑piece swimsuits, and how to interpret a swimsuit measurement chart. Following these steps will help you choose a suit that stays in place, supports your bust and hips, and feels comfortable.

How Swimsuit Sizing Works

Swimsuits are designed to hug the body closely and perform under dynamic conditions such as swimming, diving and lounging. Because the fabric stretches yet must stay secure, swimsuit sizing is more precise than with everyday clothing. Most swim brands base their swimsuit measurement charts on four key body measurements:

• Bust
• Waist
• Hips
• Torso

If your swimsuit size is off, you’ll feel it right away (and you may even accidentally expose yourself).

How To Measure Yourself To Find Your Swimsuit Size

Accurate swimsuit measurements start with having the right tools. Grab a flexible tape measure and, if possible, a friend to help with hard‑to‑reach areas. Stand in front of a mirror wearing only your undergarments or a well‑fitting bra. 

Keep your posture natural—don’t suck in your stomach or arch your back—and ensure the tape remains level and snug against your skin. Take each of the following measurements twice and average the numbers if they differ.

Measuring Your Bust

1. Wear a non‑padded bra and relax your arms at your sides.
2. Wrap the tape around the fullest part of your bust, typically at nipple level. Keep the tape parallel to the floor and avoid pulling it too tight.
3. Record the measurement in inches or centimeters.

This is your bust measurement, and it determines your bikini top size and how much room you’ll need in the upper part of a one-piece swimsuit.

Measuring Your Waist

1. Find your natural waist by bending to one side; the crease marks the narrowest part of your torso.
2. Wrap the measuring tape around this point, keeping it snug but not constricting.
3. Breathe normally and measure at the end of an exhale for accuracy.

Write down this number as your natural waist measurement, which will determine the fit of high-waisted bikini bottoms and shaping one-piece styles.

Measuring Your Hips

1. Stand with your feet together.
2. Measure around the fullest part of your hips and buttocks, usually 7–9 inches below your waist.
3. Ensure the tape stays level across your backside and doesn’t twist.

Record this as your hip measurement. This number is most important for bikini bottom sizing and the lower half of one-piece swimsuits.

Measuring Your Torso

1. To measure your torso for a swimsuit one-piece, start at the top of one shoulder, where a swimsuit strap would sit.
2. Run the tape down the front of your body over the bust, between your legs, and up your back to meet the starting point.
3. Keep the tape snug but not tight; it should follow your body’s curves.

Write down the full loop measurement (circumference). This is your torso length, and it determines whether a one-piece will pull, sag, or fit comfortably.

Use Your Swimsuit Measurements To Pick Your Sizing

Once you have your measurements, the next step is to compare them to the brand’s swimsuit sizing chart. If your bust, waist, and hips fall into different sizes, start with the measurement that places you in the largest size so the suit doesn’t feel too tight or restrictive.

For example, if your bust measures as a Medium, your waist measures as a Small, and your hips measure as a Medium, choose a Medium for the most comfortable swimsuit fit.

Swimsuit Measurement Chart

Most swimwear sizing charts list body measurement ranges for each size. These numbers represent the bust, waist, and hip measurements the suit is designed to fit, not the measurements of the swimsuit itself. While exact sizing varies by brand, the chart below shows common measurement ranges used in women’s swimsuit sizing.

How To Measure Your Bikini Size

To find your bikini size, you’ll use the same swimsuit measurements listed above, but you’ll evaluate the top and bottom separately. Many swimwear brands sell swim separates (also called mix-and-match bikini sets). Instead of purchasing a fixed-size set, you can select your top and bottom individually. This allows you to choose different sizes for each piece based on your bust, waist, and hip measurements, creating a more accurate and comfortable fitting swimsuit.

Measuring Bikini Tops

Bikini tops cover the chest area and follow a similar sizing to that of bras, so they’re usually mentioned as 32A, 34B, 36C, and so on. The numbers represent the band (underbust) measurement, whereas the letters refer to your cup size. If you don’t know your bra size, you can measure bikini top sizing like this:

• Band Size: Wrap the tape firmly around your rib cage, just under your bust. Add about 5 inches to this measurement to determine your band size (round down to the nearest even number if necessary).
• Cup Size: Measure around the fullest part of your bust. Subtract your band measurement from your bust measurement; each inch of difference corresponds to a cup size (1 inch = A, 2 inches = B, and so on).

If you’re between sizes, look for adjustable straps or tie-back bikini tops for flexibility. Underwire styles should lie flat against the rib cage. If you see any gapping, that means the cup or band is too big.

Measuring Bikini Bottoms

Bikini bottoms fit more like underwear than pants. Because swim fabric stretches and hugs the body, sizing is typically closer to your regular panty size.

However, bikini sizing systems vary by brand. Some use numerical sizing (2, 4, 6, 8, 10), while others use standard labels like XS, S, M, L, and XL. When shopping for swim separates, check the bottom-specific size chart and compare it to your waist and hip measurements. Avoid relying on your usual jeans size, since denim sizing and swimsuit sizing are very different.

If you’re between sizes, consider the level of coverage you prefer. A smaller size offers a more snug and revealing fit, while sizing up can provide slightly more comfort and coverage.

How a Swimsuit Should Fit

Taking accurate measurements is the first step in swimsuit sizing. The next step is understanding how a properly fitted swimsuit should actually feel and look once it’s on your body.

Bust Swimsuit Fit

For both bikinis and one-piece swimsuits, the bust area should feel supported and secure.

• The fabric should lie flat against your chest without gaping.
• Underwire (if present) should sit flush against your rib cage.
• There should be no spillage over the top or sides of the cups.
• Straps should stay in place without digging into your shoulders.

If you notice gapping, the cup or band may be too large. If you experience bulging or discomfort, you may need to size up based on your bust measurement.

Waist and Midsection Swimsuit Fit

Around the waist, the swimsuit should contour to your shape without creating deep indentations.

• The fabric should smooth across your stomach.
• You should be able to breathe and move comfortably.
• There should be no rolling or folding at the waistline.

High-waisted bikini bottoms should sit securely at your natural waist without sliding down when you move.

Hip and Bottom Swimsuit Fit

At the hips and seat, the swimsuit should stay in place when you walk, sit, or bend.

• The leg openings should lie flat without cutting into your skin.
• The back coverage should feel secure without riding up.
• The fabric should not sag or wrinkle across the seat.

If the suit feels tight across your hips or pulls when you move, your hip measurement may place you in a larger size on the swimsuit measurement chart.

Torso Fit (For One-Piece Swimsuits)

Torso length is especially important for one-piece swimsuit sizing.

• The suit should rest smoothly over your shoulders without pulling.
• There should be no downward tension at the neckline.
• The leg openings should not feel strained.
• The suit should not bunch or wrinkle at the midsection.

If a one-piece swimsuit pulls at the shoulders or feels tight from top to bottom, the torso length may be too short. If it wrinkles around the stomach or lower back, the torso may be too long.

Swimsuit Movement Test

Before removing tags, try a simple movement check:

• Raise your arms.
• Twist your torso.
• Sit down and stand back up.

Your swimsuit should remain secure and comfortable through each movement. It should not shift excessively, expose coverage areas, or require constant adjustment.

When your measurements align with the brand’s swimsuit sizing chart and the suit passes these fit checks, you can feel confident that you’ve chosen the right size for both comfort and performance.

Find the Right Swimsuit Fit With a Size Chart App Built for Apparel Brands

If you’re selling sportswear online, the more confident your shoppers feel about their measurements, the more confident they’ll feel placing an order. Kiwi Sizing helps Shopify apparel brands by adding clear measurement charts, personalized fit guidance, and easy-to-manage size recommendations directly to each product page. 

For Shopify swimwear brands, that clarity directly impacts your bottom line. If you’re serious about improving conversions and reducing returns, make sizing effortless on every product page with Kiwi Sizing, a reliable Shopify size chart app. Give your customers the clarity they need and your store the professional sizing experience it deserves.