Two sizes on a chart can look completely different (say, 34D and 36C) and still hold almost the same amount. Understanding why makes shopping across brands, sales racks, and hand-me-downs far less confusing.
What “Comparing” Two Sizes Actually Means
A size comparison starts by measuring the gap in inches between the two band numbers and the shift in cup letters. Move the band up one step (2 inches) and the cup usually needs to drop one letter to hold the same volume.
The reverse going down. That’s the sister-size relationship behind most of the comparisons on this site.
When Sizes Are NOT Equivalent
Not every pair of similar-looking sizes is a sister size. A 34D and a 34DD share the same band but a real difference in cup volume.
One full cup step more room, not an interchangeable pair. Our individual comparison pages spell out exactly which kind of difference you’re looking at.
How to Use This
Start with the Sister Size Calculator to find your own equivalents, or browse Size Charts for a specific number. As we publish individual comparison guides (like a specific “34D vs 36C” breakdown), they’ll be linked from here.