Sister Size Finder

Bra Sister Sizes

Updated March 2026

Sister sizes are bra alternatives that share the same cup volume on a different band. Enter your current size to find yours instantly.

What Are Sister Sizes?

Sister sizes are bra sizes that hold the same cup volume but on a different band. When you go up one band size, you go down one cup letter — and vice versa. The cup stays the same volume; only the band changes. For a deeper look at how each cup size differs in actual volume, see our cup size comparison.

Example

32D ↔ 34C ↔ 36B

All three hold the same cup volume. The band gets progressively looser.

When to Use Sister Sizes

These alternatives are useful when your calculated size isn't available in a specific brand or style, or when a bra fits in the cup but feels slightly too tight or too loose in the band. Going to an equivalent size lets you adjust the band without losing cup fit.

The Trade-Off

Sister sizing preserves cup volume but changes the band fit. If you sister-size up (looser band, smaller cup letter), you get more room around your ribcage but the same breast coverage. If you sister-size down (tighter band, larger cup letter), you get more support but less breathing room.

Sister sizing works best within one size up or down. Going two sizes away starts to affect the cup shape and wire width enough that the fit may feel noticeably different. Make sure you're starting from an accurate measurement — see how to measure your bra size before exploring sister sizes.

When to Use Sister Sizes

Your size is sold out

If your 34C is unavailable, a 32D or 36B shares the same cup volume. The fit will differ slightly in the band, but the cup capacity is identical.

A brand runs tight or loose

Some bra brands run a full band size smaller. If your usual band feels too tight, go up one band and down one cup — you keep the same cup volume with a more comfortable band.

Between two band sizes

If your underbust measures an odd number (like 33 inches), try both 32D and 34C. They are sister sizes with the same cup volume — let the band feel decide.

Important:

Sister sizing is a shopping workaround, not a permanent fit solution. Going more than one size away from your measured size will noticeably change support and comfort. For the most accurate starting point, use our bra size calculator.

Not sure about your starting size? Use our bra size calculator to find your starting size, then come back here to find your sister sizes. For a full breakdown of what each cup letter means, see our cup size comparison.