A 36D and a 38D both carry the “D” label, but the 38D sits on a bigger band, so its cup volume is larger despite the shared letter. This is one of the most common points of confusion when comparing sizes across brands or shopping internationally.
Volume comparison
Each 2-inch jump in band size (with the same cup letter) adds roughly one estimated cup’s worth of volume. So a 38D is closer in real volume to a 36DD or 36E than to a 36D.
Practical takeaway
When comparing two “D cup” bras with different bands, don’t expect them to feel the same the 38D will hold noticeably more.
Estimate the volume difference yourself with our Cup Volume Calculator, or find your closest sister size with our Sister Size Calculator.