It’s a common misconception that a B cup means the same thing on every band. A 34B and a 36B share the letter “B,” but because cup volume is relative to band size, the 36B actually holds more volume than the 34B roughly one cup’s worth more.
Why the letter alone is misleading
Cup size is the difference between your bust and band measurement, not an absolute volume. A bigger band with the same letter has grown proportionally, so the real-world size is larger.
How to choose between them
Compare your actual underbust and bust measurements rather than relying on the letter. If your underbust is closer to 34 inches, the 34B is your band; if it’s closer to 36, the 36B is. Don’t pick a band size based on the cup letter matching what you’re “used to.”
Use our Bra Size by Measurement Calculator to get your accurate band and cup together, or see the difference in estimated volume with our Cup Volume Calculator.