How to Read a Bra Size Label: Numbers, Letters, and Sister Sizes Explained

Quick answer

A bra size label shows your band size (a number) and cup size (a letter or letters). The number is the measurement around your ribcage just under your bust, and the letter represents the difference between your bust and band measurements. If the label says 34B, the 34 is the band and the B is the cup. That's the core of how to read a bra size label.

Bra size labels can look like a secret code, but they're actually a simple system once you know what each part represents. Whether you're holding a tag that says 34B or 38DD, the number and letter each tell you something specific about fit.

This guide answers common questions about reading bra size labels, including what the numbers and letters mean, how to spot sister sizes, and why the same size can feel different across brands. By the end, you'll know exactly what to look for on any tag.

What do the number and letter on a bra label mean?

The number is your band size. It's based on the measurement around your ribcage, directly under your bust, and it's usually an even number like 32, 34, or 36. The letter is your cup size, which indicates the volume of your breasts relative to your band. A cup size is not a fixed volume; it changes with the band size. For example, a 34B cup holds a different volume than a 36B cup.

Understanding this relationship is key to understanding bra sizes. If you go up a band size, you typically need to go down a cup size to maintain the same volume. That's where sister sizes come in, which we'll cover next.

• Band size is the number; cup size is the letter.
• Cup volume is relative to band size, not absolute.

What are sister sizes and how do they work?

Sister sizes are alternate bra sizes that hold roughly the same cup volume but have different band lengths. For example, if you wear a 34B, your sister sizes are 32C and 36A. The band goes down one size and the cup goes up one letter, or vice versa. This is useful when a bra feels close but not perfect: if the band is too tight but the cups fit well, you might try a sister size with a larger band and smaller cup.

Keep in mind that sister sizes are a starting point, not a guarantee. The fit also depends on the bra's style, brand, and your own body shape. Always check the return policy if you're experimenting with sister sizes.

• Sister sizes keep cup volume similar while changing band length.
• If the band is tight but cups fit, try a larger band with a smaller cup.
• If the band is loose but cups fit, try a smaller band with a larger cup.

Why does the same size fit differently across brands?

Bra sizing is not standardized across all brands. A 34B from one label might feel like a 34B from another, but often there are slight variations in band stretch, cup depth, and wire shape. This is why you might wear different sizes in different brands. It's not you; it's the manufacturing.

When you try a new brand, start with your usual size but be prepared to adjust. Reading the label is the first step, but the real test is how it feels and fits. Pay attention to the band, cups, and straps, and don't be afraid to try a sister size if needed.

• Brand sizing can vary; always try before you commit if possible.
• Check the brand's specific size chart if shopping online.

How do I know if the size on the label is right for me?

The label gives you a starting point, but the fit is what matters. A well-fitting bra should have a band that stays snug and level all the way around, cups that contain your breast tissue without gaps or spillage, and a center gore that lies flat against your chest. If any of these are off, the size might not be right, even if it matches your measurements.

If the band rides up in the back, it's too loose. If the cups wrinkle or gap, they're too big or the wrong shape. If you spill over the top, the cups are too small. Use these signs to adjust your size up or down, and consider sister sizes to fine-tune the fit.

• Band should be snug and level; if it rides up, go down a band size.
• Cups should lie smooth; gaps mean too big, spillage means too small.

Bra size label FAQs

What does the number on a bra label mean?

The number is the band size, which corresponds to the measurement around your ribcage just under your bust. It's usually an even number like 32, 34, or 36. If the band feels too tight or too loose, adjust the number, not the letter.

What does the letter on a bra label mean?

The letter is the cup size, representing the volume of your breasts relative to your band size. Cup sizes can be single letters (A, B, C) or double letters (DD, DDD). Cup volume changes with band size, so a 34B is not the same volume as a 36B.

How do I find my sister size?

To find a sister size, go up one band size and down one cup size, or down one band size and up one cup size. For example, if you wear 34B, your sister sizes are 32C and 36A. Use sister sizes when the band fits but the cups don't, or vice versa.

Why does my bra size vary between brands?

There is no universal sizing standard, so a 34B in one brand may fit like a 34B in another or feel completely different. Factors include band stretch, cup depth, and wire shape. Always check the brand's size chart and read reviews about fit when shopping online.

What if the label size matches my measurements but the bra still doesn't fit?

Measurements are a starting point. Fit also depends on breast shape, bra style, and personal preference. You may need to adjust the band, cup, or try a different style. If the band rides up, go down a band size; if cups gap, go down a cup size; if spillage, go up a cup size.

How real bra labels translate to fit

• Radiate Lace Full Cup Bra - Blush Black: Offered in back sizes and cup sizes, with a full cup design for full support and lasting comfort. If you know your band and cup from the label, you can select the right combination; the full cup style is ideal if you prefer more coverage.
• Convertible Full Cup T Shirt Full Bra (Nude Latte): A convertible T-shirt bra with straps that convert at the back for a crossover option, available in back and cup sizes. The label size helps you get the seamless look; convertible straps add versatility for different necklines.
• Dahlia Lace Full Cup Bra - Almond: Features wired full coverage, no padding, wider shoulder straps, and a side sling; available in back and cup sizes. If your label size indicates a fuller cup, this style's wider straps and side support can enhance comfort and shape.

Reading a bra size label is straightforward once you know that the number is your band and the letter is your cup. Remember that cup volume is relative to band size, and sister sizes can help you fine-tune the fit. Use the label as your starting point, but always trust how the bra feels and looks. With this knowledge, you can shop with confidence and find bras that truly fit.