Cup Size Comparisons Explained: A Fit Expert’s Guide
Why Cup Size Comparison Matters More Than You Think
If you’ve ever tried on a 36D in one brand and a 34DD in another—only to find that both fit—you’re not alone. Cup size confusion is incredibly common, and it’s one of the biggest barriers to finding the perfect bra or swimsuit.
At Olivia Paisley Intimates, we specialize in comfort-driven, expert-engineered support for full-busted women. That starts with fit education, including how cup sizes actually work—and how they compare across different band sizes.
Let’s demystify the alphabet soup of D, DD, DDD, and beyond.
The Truth About Cup Sizes: It’s All Relative
A common misconception is that cup sizes (like C, D, DD) indicate the absolute volume of the breast. In reality, cup size is relative to the band size.
For example:
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A 32D has less breast volume than a 36D, even though the letter is the same.
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A 34DD holds about the same volume as a 36D.
This is where the concept of sister sizing comes in.
What Are Sister Sizes?
Sister sizes are bra sizes that have the same cup volume but different band sizes. If your band is too tight but your cups fit well, you can try a sister size to get a more comfortable fit without sacrificing support.
Here’s a quick example:
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34D, 36C, and 32DD are sister sizes—they all hold similar breast volume.
Sister Size Chart Example:
| Cup Volume | Down a Band, Up a Cup | True Size | Up a Band, Down a Cup |
|---|---|---|---|
| Same | 32DD | 34D | 36C |
| Same | 34DD | 36D | 38C |
Understanding this is key when trying on different brands, styles, or bra constructions—especially in swimwear, where sizing varies even more.
D vs DD vs DDD: How Big Are These Cup Sizes Really?
Let’s break it down using 34-band as a baseline:
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34D: About 4 inches difference between bust and underbust
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34DD (E): About 5 inches difference
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34DDD (F): About 6 inches difference
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34G: Around 7 inches difference
Note: Different countries use different labeling. For example, UK sizing may go from DD → E → F → FF → G, while US brands often use DDD instead of E.
If you’ve ever wondered why a 34G UK feels different from a 34G US, this is why—it’s not just the label, it’s the system.
Common Cup Size Misconceptions
❌ All D cups are the same size
✔️ A 30D is much smaller in volume than a 38D. Band size matters.
❌ DDD = huge
✔️ Not necessarily. A 32DDD is a mid-size bust, while a 38DDD is considerably larger. The volume is relative.
❌ Going up a cup always means more volume
✔️ Only if the band stays the same. A 36D has less volume than a 34DD.
How to Find Your Best Cup Fit
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Start with a Professional Fitting
Knowing your true band and cup measurement is essential. Olivia Paisley Intimates offers fitting guides and personalized support for this reason. -
Try Sister Sizes Thoughtfully
If a bra feels tight in the band but good in the cups, go up a band and down a cup (e.g., 34E → 36DD). -
Focus on Breast Root and Shape
Cup size alone doesn’t account for shape. Wide-set, projected, or full-on-top breasts may need different cup styles even within the same size. -
Reassess Regularly
Weight changes, pregnancy, hormonal shifts, and aging can all affect your size. Refit every 6–12 months.
Why Olivia Paisley Intimates Prioritizes Fit Education
As a brand that specializes in comfort-forward, full-bust lingerie, we go beyond just offering sizes—we offer clarity. Our product development starts with understanding how real women’s bodies vary—and how best to support them.
Whether you're shopping for a 36DDD bra or a swim top for a 32G bust, understanding cup size comparisons empowers you to choose garments that feel secure, seamless, and second-skin comfortable.
Final Thoughts: Your Best Fit Is More Than a Letter
Cup size labels are just the beginning. Real fit comes from understanding the full picture—band size, cup volume, shape, and support needs. At Olivia Paisley Intimates, we’re here to guide you every step of the way with expert resources and products designed with your comfort and confidence in mind.
Need Help Finding Your True Size?
Explore our Fit Guide or chat with a Fit Expert at Olivia Paisley Intimates.
Discover how supportive, beautifully engineered bras and swimwear should really feel—no guesswork required.
