Bra Size Chart: Band, Cup, and Sister Sizes Explained
Eight out of ten women wear the wrong bra size. Two measurements, one chart, and the sister-size system fix it. Includes US/UK/EU conversion and brand-specific calibration.
Quick answers
- How to measure bra size
- Band = snug under-bust; cup = bust − band
- Cup size by difference
- 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD
- What is a sister size?
- Same cup volume, different band
- US 36C in UK
- UK 36C (same up to DD)
- US DDD in UK
- UK E
- US G cup in UK
- UK FF
Eight out of ten women wear the wrong bra size. Most of them wear a band that is too big and a cup that is too small.
The fix is two measurements taken at home in 30 seconds. Then a chart that tells you exactly which size to buy. Then the sister size system, which lets you swap to a different band-cup combo when your usual size is sold out.
Most women have never been taught any of this. The result is a drawer full of bras that pinch the back, dig the straps, ride up under the breasts, or simply don't support the body. That ends today.
This guide gives you the full bra size chart from 28A to 46K, the formula for converting a measurement into a size, the sister size table, and the US/UK/EU conversions that explain why a 32DD in America is a 32E in the UK. Plus the brand-specific calibration that decides whether a size 32C from one brand will fit you the same as a 32C from another.
How Bra Sizes Actually Work
Two numbers determine a bra size.
Band size
Cup size
A "32C" means a 32-inch band with a C cup. A "36DD" means a 36-inch band with a DD cup. The cup letter is not a fixed volume; it is a relative measurement that depends on the band.
The most misunderstood thing about bra sizing
How to Take the Measurements
Two measurements. Five minutes total. Done in front of a mirror with a soft tape.
Band measurement
Wrap the tape around your ribcage, directly under the bust. Tape parallel to the floor, snug but not tight. Wear a non-padded, non-push-up bra (or no bra). Read the number in inches.
Bust measurement
Wrap the tape around the fullest part of your bust, usually right at the nipple level. Tape parallel to the floor, snug but not compressing the breast tissue. Read the number in inches.
Both measurements should be in inches for the most reliable conversion to standard cup sizes.
The Cup Formula
Cup size = bust measurement minus band measurement.
| Difference (bust − band) | US Cup | UK Cup |
|---|---|---|
| Less than 1" | AA | AA |
| 1" | A | A |
| 2" | B | B |
| 3" | C | C |
| 4" | D | D |
| 5" | DD | DD |
| 6" | DDD or E | E |
| 7" | DDDD or F | F |
| 8" | G | FF |
| 9" | H | G |
| 10" | I | GG |
| 11" | J | H |
| 12" | K | HH |
US and UK cup naming diverges sharply at the larger sizes. A US "G" is a UK "FF." A US "K" is a UK "HH." Always check which system the brand uses.
Band Conversion: US, UK, EU
| US/UK Band | EU Band (cm) | AU Band |
|---|---|---|
| 28 | 60 | 6 |
| 30 | 65 | 8 |
| 32 | 70 | 10 |
| 34 | 75 | 12 |
| 36 | 80 | 14 |
| 38 | 85 | 16 |
| 40 | 90 | 18 |
| 42 | 95 | 20 |
| 44 | 100 | 22 |
| 46 | 105 | 24 |
Australian band sizing matches dress sizing (similar to UK), not the inch-based US/UK system. AU 12 = US 34. EU bands use centimeters and increment by 5.
Full Bra Size Chart (28A to 46K)
The bust range shows the bust circumference. Match your measured bust against your band column to find the cup.
| Band | A | B | C | D | DD | DDD | G | H |
|---|---|---|---|---|---|---|---|---|
| 28 | 30" | 31" | 32" | 33" | 34" | 35" | 36" | 37" |
| 30 | 32" | 33" | 34" | 35" | 36" | 37" | 38" | 39" |
| 32 | 34" | 35" | 36" | 37" | 38" | 39" | 40" | 41" |
| 34 | 36" | 37" | 38" | 39" | 40" | 41" | 42" | 43" |
| 36 | 38" | 39" | 40" | 41" | 42" | 43" | 44" | 45" |
| 38 | 40" | 41" | 42" | 43" | 44" | 45" | 46" | 47" |
| 40 | 42" | 43" | 44" | 45" | 46" | 47" | 48" | 49" |
| 42 | 44" | 45" | 46" | 47" | 48" | 49" | 50" | 51" |
| 44 | 46" | 47" | 48" | 49" | 50" | 51" | 52" | 53" |
| 46 | 48" | 49" | 50" | 51" | 52" | 53" | 54" | 55" |
Sister Sizes: Same Cup Volume, Different Band
A sister size is a different bra size that has the same cup volume as your usual size.
The rule
Example: 34C is the same cup volume as 32D and 36B.
Why sister sizes matter. Your usual size sells out. The bra you love only comes in the next band up. The brand has a sale but only on a different band. The sister size system lets you find a bra that fits the same chest by swapping band and cup.
How to use sister sizes
- Want a tighter band, same cup volume? Go down 1 band, up 1 cup. (34C → 32D.)
- Want a looser band, same cup volume? Go up 1 band, down 1 cup. (34C → 36B.)
Sister sizes are interchangeable for cup volume but differ in fit. The smaller-band sister will hug the ribcage more. The larger-band sister will sit looser. Choose based on which fits your ribcage best.
Common Sister Size Table
| If you wear | Sister sizes (same cup volume) |
|---|---|
| 30A | 28B, 32AA |
| 32B | 30C, 34A |
| 32C | 30D, 34B |
| 32D | 30DD, 34C |
| 32DD | 30DDD, 34D |
| 34B | 32C, 36A |
| 34C | 32D, 36B |
| 34D | 32DD, 36C |
| 34DD | 32DDD, 36D |
| 36C | 34D, 38B |
| 36D | 34DD, 38C |
| 36DD | 34DDD, 38D |
| 38C | 36D, 40B |
| 38D | 36DD, 40C |
| 38DD | 36DDD, 40D |
Use this when you can't find your usual size. The sister sizes will fit the same cup volume on slightly different bands.
Five Mistakes That Wreck Bra Sizing
Wearing the band too loose
A correct band sits horizontal across your back. If the back rides up, the band is too big. The fix is to go down 1 band size and up 1 cup (sister size).
Wearing the cup too small
Spillage out of the top, sides, or bottom of the cup means the cup is too small. The fix is to go up 1 cup size or sister-size up.
Trusting the band number from your bra label
Bras stretch with wear. A "34" bra after 6 months may fit like a 36. Always re-measure.
Skipping the bust measurement
The cup formula requires both numbers. Measuring only the band gives you no cup data.
Buying without trying on
Bras vary dramatically by brand and style. The chart gets you to the right starting size; the dressing room confirms.
How to Know If Your Bra Fits
Five quick tests.
- Band: two fingers should fit between the band and your back, no more.
- Cup: breast tissue should fill the cup with no spillage and no empty space.
- Underwire: should sit flat against your ribcage between the breasts and behind the breast tissue, never on the breast itself.
- Straps: should hold the bra up with the band doing 80% of the work. If straps are doing all the lifting, the band is too loose.
- Center gore: the fabric between the cups should sit flat against your sternum. If it floats, the cup is too small.
If any test fails, sister-size in the right direction.
Brand-Specific Sizing Notes
- Victoria's Secret: runs roomy in the band, smaller in the cup. Many shoppers size down 1 band and up 1 cup from their measured size.
- Aerie, ThirdLove: run true to standard chart. Both publish detailed fit guides for each style.
- Wacoal, Natori: premium fit. Match the chart precisely. Specific styles cater to specific bust shapes (full-on-bottom, full-on-top, even).
- Calvin Klein, Tommy Hilfiger: run roomy. Size down 1 band if between two sizes.
- Bravissimo, Curvy Kate, Panache: UK-based brands specializing in DD+ cups. Use UK cup letters (D, DD, E, F, FF, G, GG, H, HH).
- CUUP: runs slim in the band. Size up 1 band if between two sizes.
- Savage X Fenty: runs true to label. Wide range of sizes.
- Skims: runs slim, especially in the band. Size up.
Plus-Size Band Sizing
Bands above 40 follow the same chart formula. The cup-letter range expands further (G, H, I, J, K, KK, L) to accommodate larger bust volumes at the same band.
Specialty brands like Bravissimo, Goddess, and Elila publish bras up to 50J in the US system or 50KK in the UK system. The sister size rule still applies.
Sports Bra Sizing
Sports bras use a different sizing system, usually:
- S/M/L/XL letters, or
- Band-and-cup labels for high-impact and supportive sports bras.
For S/M/L sports bras, your standard band/cup determines size:
- S: 30A to 34B
- M: 32C to 36C
- L: 34D to 38C
- XL: 36D to 40C
For full-support sports bras (running, high-impact), use your band-cup measurement. The fit is closer to a regular bra than to a stretchy crop top.
FAQs
My band stretches over time. Does that mean I should size up?
No. It means you should size down to the next band when buying new bras. The new bra will fit correctly until it stretches.
Why does my US 36C not fit the same as my UK 36C?
US 36C and UK 36C are roughly the same. The divergence happens at DD+ cups. US DDD = UK E, US G = UK FF, etc.
How often should I re-measure?
Every 6 months, or after any weight change of 5 pounds or more, pregnancy, breastfeeding, or hormonal changes.
Can I wear my sister size full-time?
Yes. The cup volume is the same. The fit on your ribcage is what changes. If your sister size fits comfortably, it's a valid alternative to your "true" size.
My measurements put me at 28GG. Is that real?
Yes. Small band, large cup is a common but underserved combination. Specialty brands (Bravissimo, Curvy Kate, Cleo) make 28-32 bands in DD+ cups. Most mass-market brands skip these sizes, which is why so many women never find their right fit.
What is a sister size?
A different bra size with the same cup volume as your usual size. Go up one band, down one cup letter; or down one band, up one cup. A 34C, 32D, and 36B all have the same cup volume.
Save Your Numbers and Re-Measure Twice a Year
Three numbers and a sister size cheat sheet are all you need to shop bras online with confidence.
- Band measurement (in inches)
- Bust measurement (in inches)
- Calculated bra size (band + cup letter)
- Sister sizes (1 band up/down, 1 cup down/up)
Re-measure every 6 months. Bras stretch, bodies change. The right number today is not the right number 12 months from now. Stores running Tailor Size Guide let shoppers save these numbers and reuse them across every bra in the store.
Selling bras, intimates, or activewear on Shopify?
Bra sizing is the most failure-prone category in apparel. Tailor Size Guide adds smart band-cup calculators, sister size suggestions, and brand-specific fit recommendations to your product pages so customers find their right fit on the first order.