Swimwear sizing is notoriously inconsistent. A medium in one brand can be a small in the next, and a top that fits in the changing room may not hold up in the water.
It turns tape measurements into typical sizes, so you have somewhere to start when you open a size chart.
How to use the Bikini Calculator#
- Measure yourself. Use a soft tape measure over thin clothing or none, and keep it level and snug.
- Enter your measurements. Choose inches or centimetres and type your bust, underbust and hips.
- Read your sizes. You get a top size, a bottom size and a bra-style size.
How the sizes are chosen#
Top and bottom are chosen separately, because most people don’t fit the same size in both.
How to measure#
Stand straight and breathe out normally. For the bust, wrap the tape across the fullest point of your chest. For the underbust, measure around your ribs directly beneath the bust. For the hips, measure around the widest part of your hips and bottom. Don’t pull the tape tight.
Always check the brand’s chart#
These are general sizes. Brands differ, and styles such as triangle tops, bandeaus and high-waisted bottoms fit differently. If you’re between sizes, choose the larger for support and comfort, or look for a mix-and-match brand that sells tops and bottoms separately. If your result is in a size range that the brand doesn’t cover, look at its chart before you buy.
A worked example and sister sizes#
With a bust of 36 inches, an underbust of 31 inches and hips of 38 inches, the calculator gives a large top, a medium bottom and a 32DD in bra sizing. The band comes from the underbust, rounded to an even number (31 becomes 32). The cup comes from the difference between bust and underbust, 5 inches here, which maps to DD. If the 32DD band feels too loose or tight, try a sister size: 34D has the same cup volume with a looser band, and 30DDD has a tighter band with the same cup volume.
| Bust − underbust | Cup |
|---|---|
| 1 in | A |
| 2 in | B |
| 3 in | C |
| 4 in | D |
| 5 in | DD |
| 6 in | DDD |
What changes the fit#
Fabric stretch, lining, padding and design all affect the size you need. Tops with underwire or molded cups follow bra sizing and need a closer measurement. Triangle and bandeau tops are more forgiving, but they offer less support. Tie sides and adjustable straps let you fine-tune. Swimwear stretches when wet and slackens with sun, chlorine and age, so a snug fit in the shop may be right, while a loose one will get looser. High-waisted bottoms are cut for the waist as well as the hips, so measure the waist if the brand’s chart asks for it.
Measuring and buying online#
Use a soft tape and stand relaxed. Measure in the same underwear you plan to wear under a swimsuit pattern, or bare, and write the numbers down. Check the brand’s size chart and its return policy before you order, since sizes differ between countries: a UK size 12 is a US size 8. Read the reviews for notes on whether the brand runs small or large, and check the fabric blend: more elastane means more stretch and recovery. Many shops sell tops and bottoms separately, so you can order different sizes for each. Our BMI calculator is not a sizing tool, but if you track measurements over time, use the same method each time.
Frequently asked questions#
Measure your bust, underbust and hips and match them against a size chart. This calculator gives typical sizes.
Yes, and it’s common. Many brands sell them separately.
Size up for support, or choose a style with adjustable straps and ties.
No. Brands vary, so use the result as a starting point and check the size chart.
Measure around the fullest part of the bust and around the ribs just under the bust. The band size comes from the underbust and the cup from the difference between the two measurements. The calculator gives a general size such as S, M or L and a bra-style size for underwire tops. Always compare with the brand’s own chart.
If you are between sizes, choose the larger one for a top that needs to support you and for a comfortable bottom. Swimwear is stretchy, though, so if you like a snug fit and the fabric has a lot of elastane, the smaller size may be fine. Check the brand’s reviews and return policy before you decide.