RSLove Fit Guide
Ever looked at a bra label like 34C or 40DD and wondered what those numbers and letters actually mean? You’re not alone. Once you understand the basics, bra sizing becomes much easier to navigate.
Bra sizing is really built from two measurements: your band size and your cup size. The number tells you about the band, while the letter describes the difference between your bust and band measurements.
The important part? A cup letter does not mean the same thing across every band size. A 34C and a 38C are not the same cup volume.
Bra Size in One Sentence
In a size like 36D, “36” is the band size and “D” is the cup size. Both measurements work together to determine the overall fit.
First Things First
What Does the Number in a Bra Size Mean?
The number — such as 32, 34, 36 or 40 — refers to your band size. This is the measurement around your ribcage, just underneath the bust.
Your band provides most of the bra’s support, so it should feel secure and level around your body without digging in or riding up at the back.
Next
What Does the Letter Mean?
The letter — A, B, C, D, DD and beyond — refers to cup size. It is based on the difference between your bust measurement and your band measurement.
As that difference increases, the cup letter typically increases too. That’s why the number and letter should always be considered together.
If two people both wear a C cup but one wears a 32C and the other wears a 38C, the 38C has a larger overall cup volume because it is built on a larger band.
A Common Confusion
Is a D Cup Always “Large”?
Not necessarily. Cup size is relative to band size. A D cup on a smaller band can hold less volume than a D cup on a larger band.
This is one reason it can be misleading to talk about cup letters on their own. The full bra size — number and letter — gives you the real picture.
What Are Sister Sizes?
Sister sizes are bra sizes with similar cup volume but different band sizes. They can be useful when the cup feels right but the band feels too tight or too loose.
| Smaller Band / Larger Cup | Current Size | Larger Band / Smaller Cup |
|---|---|---|
| 32D | 34C | 36B |
| 34DD | 36D | 38C |
Sister sizing is a useful starting point, but fit can still vary depending on bra shape, fabric and construction.
Need a Starting Point?
Check the RSLove Size Guide
Compare your bust measurement with RSLove’s cup guide before choosing your size.
Fit Check
How Should a Bra Actually Fit?
A well-fitting bra should feel supportive without feeling restrictive. The band should stay level, the cups should contain the bust smoothly and the straps should sit comfortably on your shoulders.
- The back band should not ride upward.
- Cup fabric should not wrinkle or noticeably overflow.
- Straps should not do all the work.
The center and underwire should sit comfortably against the body when the bra is designed that way.
Common Signs You May Need a Different Bra Size
Your body can change over time, and so can your bra fit. It may be worth checking your size again if you notice:
- the band constantly rides up
- the cups gap at the top
- the bust spills over the cup edge
- straps keep falling down
- the bra feels much tighter or looser than it used to
Quick Answers
Bra Size FAQ
What do the numbers and letters in bra sizes mean?
The number represents the band size, while the letter represents the cup size. Both measurements work together to determine the bra’s overall size.
Is DD bigger than D?
Yes, within the same band size. For example, a 36DD has a larger cup volume than a 36D. But cup volume changes when the band size changes.
Why can I wear different bra sizes in different brands?
Bra construction, fabric stretch, cup shape and sizing standards can vary by brand. Treat your usual size as a starting point rather than a guarantee.
How often should I measure my bra size?
Recheck whenever your bras stop fitting comfortably or after noticeable body changes. Fit matters more than sticking to the same number forever.
What if I’m between two sizes?
Try both sizes when possible and compare the band, cup and overall comfort. Sister sizing can also help when the cup feels right but the band does not.
Find Your Fit
Start with the Right Size, Then Choose the Style You Love
From lace underwire sets to softer lingerie styles, knowing your measurements gives you a better starting point for finding a comfortable fit.
Looking for more sizing help?
See the Full RSLove Size Guide →