Bra Atlas fitting card
30DUK · same in the US
Measures about 30 in underbust and 34 in bust. Same cups as 28DD and 32C.
- UK
- 30D
- US
- 30D
- EU
- 65D
- FR
- 80D
- AU
- 8D
- JP
- E65
Same cups 28DD·30D·32C
30D sister sizes, conversions and measurements
30D is a small band with a D cup, and it shows the +4 method at its most misleading: the same tape measurements come out as 34AA.
Every sister of 30D
- 26ETighter band by 4 in, 2 cup letters up (US 26DDD, EU 55F)
- 28DDTighter band by 2 in, 1 cup letter up (US 28DD, EU 60E)
- 30DThis size (US 30D, EU 65D)
- 32CLooser band by 2 in, 1 cup letter down (US 32C, EU 70C)
- 34BLooser band by 4 in, 2 cup letters down (US 34B, EU 75B)
- 36ALooser band by 6 in, 3 cup letters down (US 36A, EU 80A)
28DD
tighter band
30D
your size
32C
looser band
Same cups, three bands: 28DD, 30D, 32C hold the same cup volume.
Tape measurements that give 30D
Computed by the Bra Atlas engine with the measured-band method, and checked by running each pair back through it.
| Snug underbust | Fullest bust | Result |
|---|---|---|
| 29 in (74 cm) | 33.5 in (85 cm) | 30D |
| 29.5 in (75 cm) | 33.75 in (86 cm) | 30D |
| 30 in (76 cm) | 34 in (86 cm) | 30D |
| 30.5 in (77 cm) | 34.25 in (87 cm) | 30D |
Same body, other methods: 30 in and 34 in is a 34AA with the traditional +4 method. With an odd 29 in underbust and a 33.5 in bust we print 30D; calculator.net's rule (band rounded, cup from the raw difference) would print 30DD. Why methods differ.
What is particular about 30D
"30d sister size" gets about 720 Google searches a month in the US and 170 in the UK (Google Ads data, September 2026).
Every calculator agreed, except one method
One of our 10 test measurements was 30 in underbust, 34 in bust. A Bra That Fits and calculator.net both printed 30D, and so does our engine. The +4 method pads the band to 34 and takes the cup from 34 − 34 = 0: a 34AA. A D-cup wearer told she is an AA is the clearest example of why the padded band matters.
UK, US and Europe
30D reads the same in the UK and US, EU 65D, France 80D, Australia 8D and roughly E65 in Japan, where cups run about a letter ahead.
Which sister to try
If a 30 band feels too tight, 32C holds the same cup volume on a band 2 in longer. If a 30 band rides up, 28DD is the tighter sister.
30D in every system
| UK | US | EU | FR | AU | JP (approx.) |
|---|---|---|---|---|---|
| 26E | 26DDD | 55F | 70F | 4E | G55 |
| 28DD | 28DD | 60E | 75E | 6DD | F60 |
| 30D | 30D | 65D | 80D | 8D | E65 |
| 32C | 32C | 70C | 85C | 10C | D70 |
| 34B | 34B | 75B | 90B | 12B | C75 |
| 36A | 36A | 80A | 95A | 14A | B80 |
Other sizes and tools
- Bra size calculatorCheck that 30D is still your size, with both methods shown
- Sister size chartThe full diagonal chart and fit fixes
- Fit checkTick what feels wrong in your 30D; get the size to try next
- Brand size chartsHow Victoria's Secret, ThirdLove, Wacoal, SKIMS, M&S and Freya label 30D
- D cup, explainedWhat the D cup means, and why it changes by band
- 32DDSister sizes, conversions and measurements
- 34BSister sizes, conversions and measurements
- 34CSister sizes, conversions and measurements
- 34DSister sizes, conversions and measurements
- 34DDSister sizes, conversions and measurements
- 36CSister sizes, conversions and measurements
- 36DDSister sizes, conversions and measurements
- 38DSister sizes, conversions and measurements
Sources
Each source was opened and checked on 25 September 2026. Where sources disagree, the page says so instead of picking one silently.
- A Bra That Fits calculator (community calculator of r/ABraThatFits): we submitted 18 measurement pairs in 6 systems on 25 September 2026; raw output is in our repository
- calculator.net, Bra Size Calculator: 10 measurement pairs run in a browser on 25 September 2026
- Wikipedia, "Bra size": UK and US cup ladders, the +4 method, EN 13402 and JIS cup steps
- OneMall, "Japanese Bra Size Conversion" (11 September 2026): JIS cups in 2.5 cm steps; JP letter about one above the US letter