D carries more myth than any other letter. Ask people what a D cup looks like and most will describe something large. In bra sizing it means one thing only: the bust is about 4 inches bigger than the band.
What a D cup measures
Measure snugly under the bust for the band, then loosely around the fullest part for the bust. A difference of about 4 inches is D. The letter is D in US, UK, Australian and European sizing; only the band number changes between countries.
D cup measurements for every band
| Band | US size | Bust about | UK | EU | AU | Sister sizes |
|---|---|---|---|---|---|---|
| 28 | 28D | 32 in (81 cm) | 28D | 60D | 6D | 30C |
| 30 | 30D | 34 in (86 cm) | 30D | 65D | 8D | 28DD, 32C |
| 32 | 32D | 36 in (91 cm) | 32D | 70D | 10D | 30DD, 34C |
| 34 | 34D | 38 in (97 cm) | 34D | 75D | 12D | 32DD, 36C |
| 36 | 36D | 40 in (102 cm) | 36D | 80D | 14D | 34DD, 38C |
| 38 | 38D | 42 in (107 cm) | 38D | 85D | 16D | 36DD, 40C |
| 40 | 40D | 44 in (112 cm) | 40D | 90D | 18D | 38DD, 42C |
| 42 | 42D | 46 in (117 cm) | 42D | 95D | 20D | 40DD, 44C |
| 44 | 44D | 48 in (122 cm) | 44D | 100D | 22D | 42DD |
If your numbers fall between two letters, measure again leaning forward at 90 degrees. The bra size calculator uses that third measurement to choose between them.
Why “D is big” is a myth
Two things built the myth. The first is the band. A 30D is a small bust on a narrow frame, about the same cup volume as a 34B. A 40D is a large bust, about the same as a US 34G (UK 34F). The letter is the same, the bodies are not.
The second is an old measuring habit. Some fitting methods added 4 inches to the underbust before choosing a band. That puts people in bands that are too loose and cups that are too small. A 32-inch underbust and a 38-inch bust is a 32DDD (UK 32E), but adding 4 inches gives a 36 band and a 2-inch difference: a 36B. Fitted that way, people with full busts were told they were a B or C, and D started to sound extreme. Measured without the extra inches, many people find their letter is higher than they thought and their band smaller.
Same volume, different letters
These sizes all hold about the same cup volume as a 34D: 32DD one band down, 36C one band up. The chain carries on in both directions, 30DDD and 38B. They are sister sizes: change the band, change the letter the other way, and the cup stays the same.
Styles that support a D cup
At D, cup shape and band firmness start to matter more than at B or C.
- Full cups cover and hold the most tissue and suit breasts that are full at the top.
- Balconettes lift from below and suit breasts that are fuller at the bottom.
- Molded T-shirt bras work when the shape matches; if the top gapes, try a seamed cup.
- Sports bras with separate cups (encapsulation) control movement better than pull-on styles from about D upward. See the sports bra size chart.
D cup fit problems and fixes
- Spilling at the top or sides: try DD on the same band.
- The wire sits on breast tissue at the side: the cup is too small or too narrow. Go up a cup or try a wider wire.
- The band rides up: go down a band and up a cup, 36D to 34DD.
- The center panel doesn’t touch the breastbone: the cups are too small.
Smaller: C cup. Larger: DD cup.
Sources & method: sizing rules follow the standard band-and-cup system used by UK, US, AU and EU brands, checked against fitting guides from specialist retailers and fitting communities. How we work.