Bra Fitting Encyclopedia
Bra Size Charts
In US sizing, each inch between your bust and your band is one cup letter: 1 inch is an A, 4 is a D, 5 is a DD. Below are the full cup chart, the sister-size table (same cup volume, different band), and a fit-adjustment table for the most common problems.
US cup size chart
| Difference (bust minus band) | US cup size | UK cup size, for comparison |
|---|---|---|
| 1 inch | A | A |
| 2 inches | B | B |
| 3 inches | C | C |
| 4 inches | D | D |
| 5 inches | DD or E | DD |
| 6 inches | DDD or F | E |
| 7 inches | G | F |
| 8 inches | H | FF |
| 9 inches | I (or HH) | G |
| 10 inches | J | GG |
| 11 inches | K (or I) | H |
| 12 inches | L (or K) | HH |
Sister sizes: same cup volume, different band
Read each row as one cup volume wearing different band sizes. Moving along a row keeps the volume constant while the band changes.
| Band | Sister sizes, same cup volume |
|---|---|
| 28 | 28DD, 30D, 32C, 34B, 36A |
| 30 | 30DD, 32D, 34C, 36B, 38A |
| 32 | 32DD, 34D, 36C, 38B, 40A |
| 34 | 34DD, 36D, 38C, 40B, 42A |
| 36 | 36DD, 38D, 40C, 42B, 44A |
| 38 | 38DD, 40D, 42C, 44B, 46A |
| 40 | 40DD, 42D, 44C, 46B, 48A |
How to move: band too tight with cups that fit, go up a band and down a cup (34C to 36B). Band too loose with cups that fit, go down a band and up a cup (34C to 32D). Band fits but cups are too small, go up a cup (34C to 34D). Band fits but cups are too big, go down a cup (34C to 34B).
Fit adjustment table
If your current bra does not fit, find the row that matches your symptoms. These are general patterns, not rules; always try the new size and judge by comfort.
| Current problem | Adjustment | Example |
|---|---|---|
| Band fits, cups too small | Go up a cup size | 34B to 34C |
| Band fits, cups too big | Go down a cup size | 34B to 34A |
| Band too big, cups fit | Down a band, up a cup (sister size) | 34B to 32C |
| Band too small, cups fit | Up a band, down a cup (sister size) | 34B to 36A |
| Band too small, cups too small | Up a band, keep cup letter | 34B to 36B |
| Band too small, cups too big | Up a band, down two cup sizes | 34B to 36AA |
| Band too big, cups too big | Down a band, keep cup letter | 34B to 32B |
| Band too big, cups too small | Down a band, up two cup sizes | 34B to 32D |
Three principles behind every chart
- Cup size is a ratio proportional to band size. A 28E is much smaller than a 36E.
- There is no fixed D cup. The letter only means something next to its band number.
- Most people underestimate their cup size. Going from a 32B to a 28E is normal, not a mistake.
The one-inch-per-cup convention is the broad US standard, but some brands use their own systems, and US letter mappings above DD vary between sources. Where sources disagree on the letters at 6 and 9 inches, this chart uses the more common US mapping (DDD or F at 6, I or HH at 9). See between sizes for the full set of documented conflicts.
The chart ends where the scan begins
Charts exist because bands and cups are mass-produced in steps. Radical skips the steps: each cup is made to its own side and the band is cut to your ribcage, from measurements read off two photos on your phone.
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