Duga Fashion

34B vs 36A: The Difference, Measurements & Which Fits You

Bra Size Comparisons

Last updated: August 2026

Comparing 34B and 36A: these two are sister sizes — the same cup volume carried on a different band, so the choice is about how the band feels, not how much the cups hold.

Quick answer: 34B and 36A hold the same amount in the cup. Neither is ‘bigger’ — pick the band that sits level and snug.
How we work these sizes out. Every size on this page is calculated the same way: your band is your underbust measurement (taken snugly under the bust and rounded to the nearest even size), and your cup is the difference between your bust and underbust — about one cup per inch. It is the measurement-first method recommended by professional fitters and bra-fitting communities, and it is the same maths behind our bra size calculator.

34B vs 36A at a glance

  34B 36A
Band (underbust) 33–34 in (84–86 cm) 35–36 in (89–91 cm)
Bust 36–37 in (91–94 cm) 37–38 in (94–97 cm)
Cup (US) B A
UK 34B 36A
EU 75B 80A

The band difference

36A has the wider band and 34B the narrower one — a 2-inch difference around the ribcage. The band is where most of a bra’s support comes from, so this gap changes how the bra feels far more than the letter suggests.

The cup difference

On its own band, 34B takes the larger cup letter. Remember the letter is a bust-minus-band difference, though, so cup volume also depends on the band each letter sits on.

So which one is actually bigger?

Neither, in the cup. 34B and 36A are sister sizes: the cups hold the same volume and only the band width changes. If one feels tight around your body, the other is the natural swap — same cups, roomier or firmer band. This is the most useful thing to know about the two sizes, and it is why fitters move between sister sizes so often.

When to choose 34B over 36A

  • Pick 34B if the band on your current bra rides up at the back or feels loose — a firmer band sits better and supports more.
  • Pick 36A if your band digs in, leaves marks, or you struggle to breathe comfortably — the wider band relieves the pressure while keeping the same cup.

How to check the fit is actually right

Numbers get you to the right size on paper; these hands-on checks tell you whether it fits in real life. Do them in front of a mirror, wearing the bra on the loosest hook:

  • Band: it should sit level all the way around, in line with the front. Slide two fingers under it at the back — snug, not loose, no riding up when you raise your arms. The band does roughly 80% of the support work, so this matters most.
  • Cups: do a quick “scoop and swoop” — lean forward, settle everything into the cup, then stand up. There should be no spillage over the top or sides, and no wrinkling or gaping at the edge. Spillage means size up a cup; gaping means size down a cup.
  • Centre gore: the little bridge between the cups should lie flat against your breastbone. If it floats off the body, the cup is usually too small.
  • Straps: you should fit a finger under them comfortably. If they dig in or carry most of the weight, the band is too loose — tighten it or size the band down.

34B sister sizes

Size Underbust Bust
32C 31–32 in 35–36 in
34B 33–34 in 36–37 in
36A 35–36 in 37–38 in

36A sister sizes

Size Underbust Bust
34B 33–34 in 36–37 in
36A 35–36 in 37–38 in
38AA 37–38 in 38–39 in

International conversions

34B converts to 34B (UK) and 75B (EU); 36A converts to 36A (UK) and 80A (EU). Cup letters above D differ between US, UK and EU systems, so always check a brand’s own country of sizing.

These figures are a starting point, not a guarantee of fit. Cup lettering and cut vary between brands, and bodies differ in shape as well as measurement, so always try a size on where you can. This guide is for general information and is not medical advice — if you need fitting for a medical reason (for example after surgery), see a professional fitter or clinician.
Find your own size in seconds with the bra size calculator, or read the full 34B guide and full 36A guide.

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