40H and 40I are easy to confuse on a size chart, but the jump in cup volume between them is bigger than the single letter suggests.
Why 40H and 40I Only Differ in Cup Volume
On the same band, a bigger cup letter simply means more distance between your underbust and bust measurement. Nothing about band comfort or ribcage size changes.
Which One Should You Try
If you’re between the two, cup gaping or wrinkling at the top usually means the smaller cup, while visible spillage at the top or sides points to needing the bigger one.
Not sure which is your actual size? Run your measurements through the Main Bra Calculator- free, private, under a minute.
A Quick Self-Check
Put on your current bra and raise both arms straight overhead. If the band shifts up noticeably or a cup gaps open, that’s a real clue pointing to which of the two sizes you actually need.
A Real Example
A useful comparison: two people with the exact same band size can have this exact letter difference between them and both be correctly sized. It comes down to actual tissue volume, not what “should” be normal.
A Mistake Worth Avoiding
Buying based on the number alone without trying the style. Construction varies enough between brands that the same labeled size can fit two completely different ways.
When This Comparison Actually Comes Up
People switching from a padded or push-up style to an unlined or wireless style often need to reconsider this exact comparison, since padding can mask a size that wasn’t quite right to begin with.
Brand Cut Changes the Answer Too
Fabric choice matters more than people expect: a band cut from a stiffer, less-stretch material holds its size longer, while a softer, stretchier band tends to loosen with wear faster. Both can be labeled the same size and feel completely different by month three.
Style Considerations
Balconette and demi styles tend to work well here since they don’t rely on excess fabric to create shape.
This Can Change Over Time
Weight fluctuation of even a few pounds can nudge a band size, especially at the boundary between two sizes. This isn’t a flaw in the measuring process, just how bodies naturally vary.
Shopping Tips
Reading recent reviews that mention true-to-size feedback for the exact style (rather than the brand generally) is one of the more reliable ways to predict fit before buying online.
