12 refers to the band size, designed to fit a 75 cm underbust (around your ribcage).
B refers to the cup size, accommodating a bust measurement of approximately 90 cm.

The difference between bust and underbust measurements determines your cup size. In this case, a 15 cm difference indicates a B cup volume. This size offers a snug, supportive fit that sits just right.

International Size Equivalents

Here’s a handy size conversion chart showing how 12B compares to global sizing systems. For a complete breakdown across all sizes, check out our full size conversion chart:

Region	Equivalent Size
UK	34B
US	34B
EU	75B
FR	90B

This international bra size chart helps you shop confidently, no matter where the brand originates.

How to Measure Your Bra Size

Getting the correct bra size is a piece of cake with this simple chart and fitting guide. Grab a measuring tape and follow these steps:

Measure your underbust (band size):

Keep the tape level and snug under your bust.
Around 75 cm = Size 12 band.

Measure your bust (cup size):

Measure across the fullest part of your bust.
Around 90 cm gives a 15 cm difference = B cup.

Use this fitting matrix to double-check your size:

Underbust 73–77 cm + Bust 88–92 cm = 12B.

These bust measurements ensure you're getting a true bra size fit, based on regular sizing body measurements.

Sister Sizes to Consider

If 12B feels slightly off, try a sister size for the same cup volume with a different band size:

10C: Smaller band, larger cup
14A: Larger band, smaller cup

This sister sizing method ensures comfort without compromising support.

Best Bra Styles for 12B

With a well-balanced body size and cup volume, 12B works well with a wide range of bras:

Lightly padded: Ideal for everyday lift
Wireless: All-day comfort with natural shaping
Seamless: Discreet under fitted clothing
Balconette and demi-cup styles: Highlight your neckline elegantly

These styles complement a 12B body shape without adding unnecessary bulk and are perfect for different moments in your day: seamless and wireless bras are ideal for work or lounging, lightly padded bras give you a polished silhouette for daily wear, and balconette or demi-cup styles bring elegant structure for special occasions or evening outfits.

Featured Brands That Carry 12B

At The Foundation, our curated selection of premium lingerie brands includes 12B options for every taste—whether you prefer everyday comfort or special occasion style:

Shop 12B Bras at The Foundation

Browse our complete 12B bra size collection to find premium designs tailored to your shape and size. - Looking for structure? Try our balconette and lightly padded styles.

Prefer softness? Wireless and seamless options are your go-to.
Need something versatile? T-shirt bras and everyday styles fit the bill.
Dressing up? Demi-cup and lace-detailed bras are perfect for special occasions.

Shop Now to experience lingerie that fits like it was made just for you.

FAQs

What does 12B mean in bra sizing?

It refers to a 75 cm underbust (band size) and approximately 90 cm bust measurement (cup size) in Australian sizing.

How do I know if 12B is my correct bra size?

Use a soft measuring tape to get your body measurements. If the underbust is close to 75 cm and the bust is around 90 cm, you likely wear a 12B.

What are sister sizes for 12B?

You can try 10C for a tighter band or 14A for a looser fit—both offer a similar cup volume.

Which bra styles suit 12B best?

Lightly padded, wireless, seamless, balconette, and demi-cup styles complement a 12B shape comfortably and stylishly.

Do you carry size 12B in multiple brands?

Yes! The Foundation stocks top-tier brands like Prima Donna, Simone Pérèle, Panache, and more—all with reliable size charts for accurate fit.

12B Bra Size – Find Your Perfect Fit

Understanding the 12B Bra Size