Bra Sizes S, M, L and XL: What They Mean

Letter bra sizes (XS, S, M, L, XL) are not a standard conversion from band and cup sizes. At most brands, each letter steps up roughly one band size and covers a few cup sizes: a medium is often near a 34 band with B to D cups. But brands draw the lines differently, so always use the brand’s own chart with both your underbust and bust measurements.

Where you’ll see letter sizes

• Bralettes and soft wireless bras
• Sports bras, especially compression styles
• Sleep and lounge bras
• Tank tops and dresses with built-in bras

Structured underwire bras almost always use band and cup sizes, because the wire has to match your breast’s width.

A typical pattern (check every brand)

This is only a rough guide to how letter charts tend to look. Some brands size by band only, some by bust only, and some list cup ranges for each letter. Two brands can put a 34C in different letters.

How to choose your letter size

1. Measure snugly under your bust and loosely around the fullest part. Our bra size calculator gives you a band and cup.
2. Find the brand’s chart and check where your underbust and your bust each fall.
3. If they agree, you’re done.
4. If they don’t, decide what matters more for this bra:
   • Support (sports bras): go with your band.
   • Coverage and comfort (bralettes): go with your bust.

If your band is small and your cups are big, letter sizes often fail you: the cups are too small in your band’s letter, and the band is too loose in your cups’ letter. A brand that sizes by band and cup will fit better. Our sports bra size chart explains how sports brands handle this.

Letter sizes vs band and cup

Our guides to bra band size and what bra sizes mean explain the numbered system in detail.