Getting the right size is the biggest factor in whether a swimsuit feels great or ends up in the returns pile. Swimwear fits closer to the body than most clothing, it has to stay put when wet, and it’s often sized differently from your everyday wardrobe.
This guide walks you through how to take your measurements, how common swimwear sizes convert between the US, UK and EU, and what to do when you land between two sizes. For a more detailed, step-by-step walkthrough of the measuring itself, see our guide on how to measure yourself for a swimsuit.
Before you measure
You only need a soft, flexible tape measure and a mirror. A few habits make your numbers much more reliable:
- Measure over bare skin or a thin, unpadded bra and underwear.
- Stand up straight and relaxed, with your feet together and your arms loosely by your sides.
- Keep the tape level and snug, but not tight. It should lie flat without digging in.
- Breathe normally and don’t hold your stomach in.
How to measure
Bust
Wrap the tape around the fullest part of your bust, keeping it level across your back. This is the measurement most size charts use for tops and one-pieces.
Underbust
Measure directly under your bust, where a bra band would sit. The tape should be snug and horizontal. Brands that size tops by cup and band, rather than by letter size, use your underbust together with your bust to work out your fit.
Waist
Find your natural waist, the narrowest part of your torso, usually a little above your belly button. Bend to one side and the crease that forms shows you where it is. This number matters most for high-waisted bottoms and one-pieces.
Hips
Stand with your feet together and measure around the fullest part of your hips and seat. Most brands size bikini bottoms primarily by hip measurement.
Torso length (for one-pieces)
Torso length is the measurement people most often skip, and it’s the reason many one-pieces feel too short or too baggy. Place the tape at the top of one shoulder, run it diagonally down across your front, between your legs and back up across your back to the same shoulder, making a full loop. Some brands list a torso measurement or offer “long torso” options, and this is the number to compare against.
Pro tip: Measure twice and take the average. If one measurement lands between two sizes, note that down, because it will help you choose between them later.
Swimwear size conversion chart
The table below shows widely used approximate conversions between women’s letter sizes and numeric US, UK and EU sizes. Use it as a starting point when shopping across regions.
| Letter size | US | UK | EU |
|---|---|---|---|
| XS | 0–2 | 4–6 | 32–34 |
| S | 4–6 | 8–10 | 36–38 |
| M | 8–10 | 12–14 | 40–42 |
| L | 12–14 | 16–18 | 44–46 |
| XL | 16–18 | 20–22 | 48–50 |
Important: swimwear sizes vary considerably by brand, and even between different styles from the same brand. These conversions are a general guide only. Always check the brand’s own size chart, compare it against your measurements rather than your usual clothing size, and read the product description for notes on how the style fits.
Sizing tops and bottoms separately
Many people are one size on top and another on the bottom, which is completely normal. If a brand sells bikini tops and bottoms as separates, take advantage of it and size each piece to the matching measurement: bust and underbust for the top, hips for the bottom.
For tops, pay attention to how the brand sizes them. Some use letter sizes, while others use bra-style band and cup sizes, which usually give a more precise fit if you need extra support. If that’s you, our guide to swimwear for larger busts explains which support features are worth looking for.
What to do if you’re between sizes
Landing between two sizes is common. A few guidelines can help you choose:
- Think about the style. Adjustable pieces, such as tie-side bottoms, triangle tops and halter necks, are forgiving, so you can often size down. Fixed styles, like bandeaus and high-waisted bottoms, are usually better in the larger size.
- Consider the fabric. Swimwear stretches slightly when wet and relaxes over time. A suit that feels comfortably snug when dry often fits well in the water, but one that feels loose dry will only get looser.
- Prioritize your fit priority. If you plan to swim laps, surf or play beach sports, a closer fit stays in place better. For lounging, comfort may matter more than a snug fit.
- For one-pieces, go by torso and bust. If you’re long in the body, the larger size or a long-torso option is often the better choice even if your hips match the smaller size.
- Read the brand’s fit notes. Many brands state whether a style runs small, large or true to size. That advice is specific to the product and more useful than any general chart.
Pro tip: When in doubt, order both sizes from a retailer with free or easy returns, try them on at home with the hygiene liner in place, and send back the one that doesn’t fit.
Signs a swimsuit fits well
Once your suit arrives, check it in front of a mirror and move around a little: bend, squat, lift your arms and twist. A good fit usually means:
- Straps stay in place without digging into your shoulders.
- The top covers and supports your bust without gaping or cutting in at the sides.
- The band of the top sits level and doesn’t ride up at the back.
- The leg openings and waistband lie flat without pinching or leaving deep marks.
- A one-piece doesn’t pull down at the shoulders or bunch at the stomach.
If you notice any of these problems, try the next size or a different cut. Sometimes the size is right, but the style simply isn’t the best match for your shape.
Measurements change over time, so re-measure each season before you shop.