Sports bras are sized differently from everyday bras: many come in letters from XS to 4X instead of a band and cup. That makes choosing the right size feel like guesswork. This calculator starts with the measurements you would take for any bra, works out your regular size and then reads the matching alpha size off Nike’s published sports bra chart.
How to use the sports bra size calculator
- Measure the underbust snugly around the ribcage under the bust.
- Measure the bust around the fullest part, over an unlined bra if you can.
- Enter both in inches or centimetres.
- Read the results: your regular band and cup, and the Nike alpha size.
Sports bra size formula
cup = bust − band, in inches (1 = A, 2 = B, 3 = C, 4 = D, 5 = DD/E, 6 = DDD/F, 7 = G)
alpha size = Nike chart lookup on band and cup
The band and cup follow the method in the Wikipedia bra measurement article (retrieved 2026-10-15), which rounds the underbust to an even number and subtracts the band from the bust. The alpha sizes are from the Nike women’s bra size page. Note that Nike’s own measuring tool asks for different readings, so the results here convert a bra size you already know or can calculate.
| Alpha size | Band/cup A–E (Nike chart) |
|---|---|
| XXS | 28A–28E, 30A–30E |
| XS | 32A–32B |
| S | 32C–32E, 34A–34C |
| M | 34D–34E, 36A–36C |
| L | 36D–36E, 38A–38C |
| XL | 38D–38E, 40A–40C |
| XXL | 40D–40E, 42A–42C |
| 1X | 42D–42E, 44A–44C |
| 2X | 44D–44E, 46A–46C |
| 3X | 46D–46E, 48A–48C |
| 4X | 48D–48E, 50A–50C |
For cups F and G, Nike’s Alpha/Cup chart lists one size per band: 30F–30G is an XS, 32F–32G an S, 34F–34G an M, and so on up to 48F–48G, a 4X.
Worked example
Underbust 33 in, bust 38 in.
- Band: 33 is exactly between 32 and 34 and rounds up to 34.
- Cup: 38 − 34 = 4 inches, a D, so the regular size is 34D.
- Nike chart: 34D–34E is in M.
Checking the fit
- Band: it should sit level on your ribs, stay put when you raise your arms, and let two fingers slide underneath.
- Straps: secure but not digging or slipping.
- Coverage: the fabric should cover you without gaping or bulging.
- Support: do five jumping jacks; if there is too much bounce, choose a higher-support style.
Other brands use their own letters. If you need a size in another country, use the Bra Size Converter (US/UK/EU/AU/FR/JP); for sister sizes see the Sister Size Calculator. This page is general information, not a professional fitting.
Sources
Every figure above comes from these pages, read directly on the dates shown. Brand names are used only to identify published charts.
- Nike — women’s bra size chart (alpha sizes from band and cup, fit tips) — checked 2026-10-15
- Wikipedia — Brassiere measurement (band and cup method) — checked 2026-10-15
Frequently asked questions
How do I find my sports bra size?
Start from your usual bra size. Measure under the bust for the band and around the fullest part for the cup, then look it up on the brand’s chart. Nike’s chart pairs band and cup ranges with alpha sizes: 34D–34E is a medium, 36A–36C is also a medium.
Why does the sports bra size use letters?
Sports bras are often stretchy and sold in S, M, L rather than band and cup, so one size covers a range of bands and cups. The Nike chart shows that, for example, a 32C and a 34A are both a small.
What if I am between sizes?
Nike’s fit tips: the underband should stay put when you raise your arms and have room for two fingers underneath, the straps should not dig or slip. If it is too loose or tight, try the neighbouring size.
Does this cover compression and encapsulation styles?
The chart is for Nike sports bras, and different support styles fit differently. Do the five jumping jacks test that Nike suggests and move up in support if there is too much bounce.
Where are cups F and G on the chart?
Nike lists cups F (DDD) and G (DDDD) in a separate Alpha/Cup range, one size per band: 34F–34G is a medium. For other brands use the Bra Size Converter (US/UK/EU/AU/FR/JP).