I built this bra size calculator because guessing between a tighter band and a bigger cup is exhausting. Enter snug underbust and standing bust, then tap Find my size. You will get a best starting size, two sister sizes, and quick notes. Sister sizes keep cup volume the same while band fit changes, think 32DDD to 34DD.
If cups still feel off after you calculate, fix shape first
Match the cup edge to your neckline and breast root, compare balconette vs plunge, then skim brand notes before you add to cart, check brand fit notes.
Bra Size Calculator
Bra Size and Sister Size Finder
Enter your snug underbust and standing bust. We will suggest a starting size, sister sizes up and down, plus quick fit notes.
Developer self tests
How to measure, the quick version
- Choose your unit, centimeters or inches.
- Snug underbust, wrap the tape around your ribcage under the bust. Exhale gently, keep the tape level and snug, not painful.
- Standing bust, wrap the tape around the fullest point. Keep the tape level, do not squash.
- Tap Find my size, then use Copy results so you can paste your size into Notes or your cart.
This tool supports bra size by measurements in centimeters and inches. If the numbers look wild, check the unit toggle and try again.
How I use it in real life
I tried a T shirt bra from a firm band brand. My measurements gave me 32DDD/F as the best starting size. The bra size converter also showed 30G as the tighter band sister and 34DD/E as the looser band sister. I kept the 32 for most days and the 34 for long work days. No pinching, no gaping.
Sister sizes, in plain words
Cup letters are volume. Change the band and you adjust the letter to keep cup volume steady.
- Tighter band, up a cup keeps cup volume the same.
- Looser band, down a cup also keeps cup volume the same.
Mini sister chart
- 30G ↔ 32DDD
- 32DD ↔ 34D
- 36C ↔ 34D
Use the tighter sister when the band rides up. Use the looser sister for comfort or when straps are digging in.
Next steps, finish the fit and keep shopping simple
You have a starting size. Now make it work across styles and brands, then carry it into outfits.
- Dial cup shapes, match edges to your tissue, compare balconette vs plunge.
- Convert clothing sizes, shop across regions with one map, convert US, UK, EU, AU, JP.
- Plan smarter outfits, buy fewer pieces that work harder, calculate cost per wear.
Quick fixes for common fit problems
- Cups gaping at the top, try the tighter band sister, or a demi bra or balconette bra that is more open on top.
- Cup spillage at the center, try the looser band sister so the wires sit flat, or a plunge bra with a narrow center.
- Band rides up, go tighter in the band, look for three hook backs.
- Straps digging in, let the band carry more work, or try styles with wider straps and U back wings.
- Center gore not lying flat, move to the looser sister, or try a plunge if your breast root is close set.
If you want a deeper bra fit guide, open the related links under your results.
Style ideas by cup group
- Shallow to moderate cups, AA to C
Demi and balconette for lift without gaping, unlined lace for comfort, plunge for open necklines. - Moderate to full cups, D to F
Three part cups for a round shape, T shirt bra with a firm band, plunge for V neck tops. - Fuller cups, G and up
Full cup bra with reinforced wings, side support bra designs, minimizer bra for smooth lines, U back straps for stability.
Small bra size chart facts that help
- Cup steps often track about one inch of difference between bust and underbust in imperial.
- In metric, about 2.5 cm per cup step is a useful shortcut.
- What does DD mean in bra size It is simply two steps above D, a volume label, not a judgment.
For region jumps, scan our international bra size conversion notes. You will see US to UK bra size, UK to US bra size, and EU to US bra size patterns that help when you shop outside your home region.
What your result means
When you hit Find my size, you will see:
- Best starting size, the one to order first.
- Tighter band sister, down one band, up one cup.
- Looser band sister, up one band, down one cup.
- Quick fit notes, for example, fuller cup, try side support.
- Style ideas, three shapes that tend to work for your cup group.
Open two tabs, your best size and one sister size. If a product page says runs small in the band, try the looser band sister. If it says stretchy band, try the tighter band sister.
Care and lifespan, because fit changes over time
- How to wash bras, cool water in a mesh bag, clasp closed, then lay flat to dry.
- Adjust straps after the first wash, bands relax slightly.
- How often to replace bras, plan on 6 to 12 months in normal rotation.
FAQ
Is 34DD the same as 32DDD?
They are sister sizes with similar cup volume. The 32 band fits tighter, the 34 band fits looser.
32DDD to 34DD sister size?
Yes, that is the looser band sister. 30G sister size is the tighter band sister.
How tight should a bra band be?
Two finger test, two fingers should fit under the back band, not three.
How to tell if a bra fits?
Wires sit flat at the center, the band is level, straps rest without digging, cups are smooth with no gaping or spill.
Do brands size the same?
No. Blocks and fabrics vary. Use your starting size, then adjust with the two sister sizes the tool gives you.
Can I use EU or UK sizes here?
Yes. Use the finder for band and cup, then check our international bra size conversion notes for US to UK bra size and EU to US bra size jumps when you shop abroad.
Ready to find your size
Enter your snug underbust and standing bust in the sister size finder above, then copy your starting size and sister sizes. Try one T shirt bra and one balconette, see which style smiles back at you, and save the result so your next checkout is painless.
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Iskra Banović is our seasoned Editor-in-Chief at Blufashion. She has been steering the website’s content and editorial direction since 2018. With a rich background in fashion design, Iskra’s expertise spans across fashion, interior design, beauty, lifestyle, travel, and culture.
