Bikini tops are sold in simple sizes such as S, M and L, but your bra size is a band and a cup. Mapping one to the other is where most mistakes happen. This calculator starts from either your bra size or your bust measurement and reads the bikini top size from a published swimwear chart, with the clothing sizes it covers.
How to use the bikini top size calculator
- Choose what you know: your bra size, or your bust measurement.
- Enter the band and cup, or measure around the fullest part of the bust, tape level, and enter the number.
- Read the result: the bikini top size, the numeric clothing sizes, and the bra sizes and bust range the size covers.
Bikini top size formula (chart lookup)
or: size = first size whose upper bust limit ≥ your bust
a measurement between two sizes → the larger size
The chart is the Vanilla Beach swimwear size chart published by Target (retrieved 2026-10-15). It lists, for each size, the bust, waist and hip measurements and the bra sizes covered. Target’s note applies to the fit: tops with an adjustable back tie fit bands of 30 to 38 inches, and tops with a hook or no closure fit bands of 32 to 36 inches.
| Size | Numeric | Bust (in) | Waist (in) | Hip (in) | Bra sizes |
|---|---|---|---|---|---|
| XS | 1 | 31.5 | 25.5 | 34.5 | 32A |
| S | 3–5 | 32.5–33.5 | 26.5–27.5 | 35.5–36.5 | 32B, 34A |
| M | 7–9 | 34.5–35.5 | 28.5–29.5 | 37.5–38.5 | 34B, 34C, 36A, 36B |
| L | 11–13 | 37–38.5 | 31–32.5 | 40–41.5 | 36C, 38B |
| XL | 15–17 | 40–41.5 | 34.5–36.5 | 43–44.5 | 38C |
Worked example
Bra size 34C.
- 34C appears in the medium row: 34B, 34C, 36A, 36B.
- Bikini top size: M, numeric clothing size 7–9, bust 34.5–35.5 in.
- If instead you only know your bust and it is 34.25 in (87 cm), that is above the 33.5 in limit of S and within the 35.5 in limit of M, so the answer is also M.
Buying swimwear tops
- Underwired versus unwired: underwired tops use bra sizing; stretch tops use S–XL.
- Two sizes are normal: many people wear a different size on top and bottom. Buy them separately where possible.
- Fabric stretches when wet, so choose a snug fit when trying on.
- Charts differ: Nike’s swimsuit bust ranges, for example, do not match Target’s, so use the chart of the brand you are buying from.
For one-piece and bottom sizes see the Swimsuit Size Calculator; for strapless styles see the Strapless Bra Size Calculator. This page is general guidance, not a guarantee of fit.
Sources
Every figure above comes from these pages, read directly on the dates shown. Brand names are used only to identify published charts.
- Target — Vanilla Beach women’s swimwear size chart (bust, waist, hip, bra sizes) — checked 2026-10-15
- Nike — women’s swimsuit size chart (for the cross-check) — checked 2026-10-15
Frequently asked questions
How do I find my bikini top size?
Start from your bra size or your bust measurement and read the size off a swimwear chart. On the Target chart a 34B, 34C, 36A or 36B is a medium. Shops that sell bra-sized swimwear say to order the same size as your everyday bra.
Why does one letter size cover several bra sizes?
Bikini tops are stretchy and often unlined, so one size has to fit a range of bust sizes. A medium covers four bra sizes on Target’s chart, from 34B to 36B.
Does the closure matter?
Yes. Target notes that swim tops with an adjustable back tie fit band sizes 30–38 inches, while tops with a hook closure or none fit bands 32–36 inches.
What if my bra size is not on the chart?
The chart covers 32A to 38C. For other sizes look for bra-sized swimwear or use a brand’s own chart. Nike’s swimsuit chart uses a different set of bust ranges, so charts do not match between brands.
Do I need the same size for the bottom?
Not usually. Bikini bottoms are sized by waist and hips. The Swimsuit Size Calculator covers them. Use the Bra Size Converter (US/UK/EU/AU/FR/JP) if your bra size is in another country’s system.