Bras size calculator
Bra sizes: calculate & convert
Enter your underbust and bust measurements to get your bra size — or convert a size you already wear into UK, US and French sizes.
Bra sizes conversion: the short answer
A bra size is made up of a band and a cup. The band is your underbust measurement in cm, rounded to the nearest 5 (band 75 = 73–77 cm). The cup comes from the difference between bust and underbust: 12–14 cm = A, 14–16 cm = B, 16–18 cm = C, 18–20 cm = D — every further cup step adds another 2 cm. In the UK and US the band is given in inches: EU 75C = UK/US 34C = FR 90C.
Bra size chart: band sizes worldwide
| US | UK | EU | FR | Underbustcm |
|---|---|---|---|---|
| 28 | 28 | 60 | 75 | 58–62 |
| 30 | 30 | 65 | 80 | 63–67 |
| 32 | 32 | 70 | 85 | 68–72 |
| 34 | 34 | 75 | 90 | 73–77 |
| 36 | 36 | 80 | 95 | 78–82 |
| 38 | 38 | 85 | 100 | 83–87 |
| 40 | 40 | 90 | 105 | 88–92 |
| 42 | 42 | 95 | 110 | 93–97 |
| 44 | 44 | 100 | 115 | 98–102 |
| 46 | 46 | 105 | 120 | 103–107 |
| 48 | 48 | 110 | 125 | 108–112 |
Cup chart: bust minus underbust
| Difference | US | UK | EU |
|---|---|---|---|
| 10–12 cm | AA | AA | AA |
| 12–14 cm | A | A | A |
| 14–16 cm | B | B | B |
| 16–18 cm | C | C | C |
| 18–20 cm | D | D | D |
| 20–22 cm | DD/E | DD | E |
| 22–24 cm | DDD/F | E | F |
| 24–26 cm | G | F | G |
| 26–28 cm | H | FF | H |
| 28–30 cm | I | G | I |
| 30–32 cm | J | GG | J |
The UK and the US use the same band sizes. French bands run 15 above the EU numbers.
Sister sizes: same volume, different band
A cup letter is not a fixed volume — it depends on the band. A 75C holds the same cup volume as a 70D or an 80B. These sister sizes help when the cup of a bra fits but the band is too tight or too loose:
- Band too tight, cup fine → go one band up and one cup down (75C → 80B).
- Band too loose, cup fine → go one band down and one cup up (75C → 70D).
Does your bra fit? The checklist
- Band: sits level and firm — it carries most of the weight. Two fingers fit underneath.
- Underwires: enclose the breast completely and rest on the ribcage at the root of the breast, not on breast tissue.
- Cups: no wrinkles and no gaps, and nothing spilling over the edge.
- Center gore: lies flat against the breastbone.
- Straps: do not dig in and do not slip. If you have to tighten them a lot, you usually need a firmer band.
Fasten a new bra on the loosest hook — the band stretches over time, so you can take it in later.
Measuring correctly for your bra size
Measure wearing an unpadded bra or no bra at all, standing upright and breathing normally. Take the underbust snugly right below the breasts, and the bust at its fullest point with the tape resting loosely. Both times the tape measure runs level around your back.
Tips for getting the size right
Mind your cycle
Breasts can change over the course of your cycle. Measuring mid-cycle gives the most typical result.
Measure again regularly
Weight changes, pregnancy, breastfeeding and age all change your size. Measure at least once a year.
Reading UK cups
British brands use doubled letters such as DD, FF or GG. A UK DD is an EU E.
FAQ about bra sizes
What is a 75B in UK sizes?
EU 75B is a UK 34B and a US 34B, and a 90B in France.
What bra size is a 78 cm underbust and a 94 cm bust?
The band is 80 (an underbust of 78 cm falls between 78 and 82 cm) and the difference is 16 cm. That makes it cup C — an 80C. Use the calculator above with your own numbers.
Is a UK DD the same as an EU D?
No. A UK DD is an EU E. From cup D upward, the UK, US and EU letters drift apart.
What are sister sizes?
Sister sizes have the same cup volume on a different band, for example 70D, 75C and 80B.
Should I measure with or without a bra on?
You get the most accurate numbers wearing a well-fitting, unpadded bra or nothing at all. Padded styles distort the bust measurement.