UK Bra Size Calculator
Enter your underbust and bust measurements to get an estimated UK bra size.
How the UK bra size system works
UK bra sizing is built from two parts: a band size (the number, such as 30, 32, 34) and a cup size (the letter, such as D, DD, E, F). The band comes from your underbust measurement, and the cup is based on the difference between your bust and your band size.
This calculator gives you a practical starting point for bra shopping in UK sizing. Because brand construction and fabric stretch vary, it is normal to try one or two nearby sizes before finding your best fit.
How to measure correctly at home
1) Underbust
- Wrap the tape measure directly under your bust.
- Keep it level around your body and pull it snug (not painfully tight).
- Take the number while breathing out gently.
2) Full bust
- Measure around the fullest part of your bust.
- Keep the tape level and relaxed (not compressing breast tissue).
- Wear a non-padded bra for best accuracy.
UK cup progression reference
UK brands commonly follow this cup sequence:
| Bust - Band Difference (inches) | UK Cup |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD |
| 6 | E |
| 7 | F |
| 8 | FF |
| 9 | G |
| 10 | GG |
| 11 | H |
Sister sizes: useful when fit is close
If your calculated size is almost right but not perfect, try sister sizes. Sister sizes keep a similar cup volume while changing band tension:
- Band up one step (+2): go down one cup letter.
- Band down one step (-2): go up one cup letter.
Example: if 34E feels too tight in the band, try 36DD. If 34E feels too loose in the band, try 32F.
Signs your bra size may be wrong
- Band rides up your back.
- Cups wrinkle, gape, or cut in at the top.
- Underwire sits on breast tissue instead of around it.
- Straps carry all the weight and dig into shoulders.
- Center gore does not sit flat against your sternum (for wired bras).
Helpful fitting tips for UK shoppers
Check the band first
The band does most of the support work. It should feel firm on the loosest hook when new. Over time, as elastic relaxes, you can tighten to middle and inner hooks.
Then adjust cup and shape
Different bra styles (balcony, plunge, full cup, T-shirt bra, bralette) fit differently even in the same size. If one style feels off, try another cut before assuming the size is wrong.
Re-measure regularly
Body shape can change with weight fluctuation, hormones, menstrual cycle, pregnancy, breastfeeding, menopause, and training. Re-check your size every few months for best comfort.
Frequently asked questions
Is this calculator 100% exact?
No calculator can replace trying bras on. This gives a strong starting point, then you fine-tune based on actual fit and brand differences.
Can I use cm or inches?
Yes. The tool accepts both and converts automatically for UK size calculations.
Why do UK cup letters look different from EU/US sizes?
Each region uses a different progression. UK uses double letters like DD, FF, GG, HH, while EU typically uses a more linear progression. Always verify the sizing system on the product label.
Final note
Use this UK bra size calculator as your baseline, then test nearby sister sizes for the best real-world fit. Comfort, support, and shape all matter—and the right bra should feel secure without pain.