Bra Size Calculator
Bra size calculator: a snug underbust and a bust measurement in inches or cm give a US and UK size, the EU band, how it was worked out and sister sizes. How it works
Use the Bra Size Calculator
About the Bra Size Calculator
A 34 in underbust and a 37 in bust come out as 34C in US and UK sizing. The band is the snug underbust rounded to the nearest even inch, and the cup is one letter for each inch between bust and band. This bra size calculator also shows the sister sizes, 36B and 32D, and the European band for your underbust, 85. Brands cut differently, so treat the result as the first size to try on.
Cup letter by bust minus band, US and UK
| Bust minus band | US cup | UK cup |
|---|---|---|
| Under 1 in | AA | AA |
| 1 in | A | A |
| 2 in | B | B |
| 3 in | C | C |
| 4 in | D | D |
| 5 in | DD/E | DD |
| 6 in | DDD/F | E |
| 7 in | DDDD/G | F |
| 8 in | H | FF |
| 9 in | I | G |
The difference is rounded to a whole inch first. US and UK letters agree up to D and part ways from 5 in. The chart stops at 9 in.
Band size by underbust measurement
| Underbust in inches | Underbust in centimeters | US and UK band by this method | EU band |
|---|---|---|---|
| 26 to 27 in | 63 to 67 cm | 26 | 65 |
| 28 to 29 in | 68 to 72 cm | 28 | 70 |
| 30 to 31 in | 73 to 77 cm | 30 | 75 |
| 32 to 33 in | 78 to 82 cm | 32 | 80 |
| 34 to 35 in | 83 to 87 cm | 34 | 85 |
| 36 to 37 in | 88 to 92 cm | 36 | 90 |
| 38 to 39 in | 93 to 97 cm | 38 | 95 |
| 40 to 41 in | 98 to 102 cm | 40 | 100 |
| 42 to 43 in | 103 to 107 cm | 42 | 105 |
| 44 to 45 in | 108 to 112 cm | 44 | 110 |
The band here is the underbust with no inches added. A measurement between the whole inches goes to the nearest even band, so 35.2 in is a 36. Labels that add 4 to the underbust read 4 higher for the same underbust.
Bra size from underbust and bust, US label
| Bust compared with underbust | Underbust 30 in | Underbust 32 in | Underbust 34 in | Underbust 36 in | Underbust 38 in |
|---|---|---|---|---|---|
| Same as underbust | 30AA | 32AA | 34AA | 36AA | 38AA |
| 1 in more | 30A | 32A | 34A | 36A | 38A |
| 2 in more | 30B | 32B | 34B | 36B | 38B |
| 3 in more | 30C | 32C | 34C | 36C | 38C |
| 4 in more | 30D | 32D | 34D | 36D | 38D |
| 5 in more | 30DD/E (UK 30DD) | 32DD/E (UK 32DD) | 34DD/E (UK 34DD) | 36DD/E (UK 36DD) | 38DD/E (UK 38DD) |
| 6 in more | 30DDD/F (UK 30E) | 32DDD/F (UK 32E) | 34DDD/F (UK 34E) | 36DDD/F (UK 36E) | 38DDD/F (UK 38E) |
| 7 in more | 30DDDD/G (UK 30F) | 32DDDD/G (UK 32F) | 34DDDD/G (UK 34F) | 36DDDD/G (UK 36F) | 38DDDD/G (UK 38F) |
| 8 in more | 30H (UK 30FF) | 32H (UK 32FF) | 34H (UK 34FF) | 36H (UK 36FF) | 38H (UK 38FF) |
| 9 in more | 30I (UK 30G) | 32I (UK 32G) | 34I (UK 34G) | 36I (UK 36G) | 38I (UK 38G) |
Calculator results. The UK label is given where it differs from the US one.
European cup letter by bust minus underbust
| Bust minus underbust | EU cup |
|---|---|
| 10 to 12 cm | AA |
| 12 to 14 cm | A |
| 14 to 16 cm | B |
| 16 to 18 cm | C |
| 18 to 20 cm | D |
| 20 to 22 cm | E |
| 22 to 24 cm | F |
| 24 to 26 cm | G |
| 26 to 28 cm | H |
A reference table, as the page shows it. European charts take both measurements loosely, unlike the snug underbust the calculator asks for, and step one letter per 2 cm. It is not a conversion of the US or UK letter, and the calculator does not work out a European cup.
Fit check: signs a bra is the wrong size
| What you notice | What it usually means | What to try |
|---|---|---|
| The band rides up at the back | The band is too loose | One band size down and one cup up, the sister size (32D for a 34C) |
| A new bra only fits on the tightest hook | The band is too loose | A smaller band: a new bra should fit on the loosest hook, leaving the tighter ones for when the elastic stretches |
| The band pulls more than a few centimeters off your back | The band is too loose | A smaller band; two flat fingers should slide under it snugly |
| Breast tissue spills over the top or sides of the cup | The cup is too small | One cup size up |
| The cup gapes or wrinkles | The cup is too large, or the style does not suit your shape | One cup size down, or another style |
| The underwire sits on breast tissue | The cup is too small | One cup size up |
| Straps dig in or slip, or your shoulders ache | Usually a loose band, so the straps carry the weight | Fix the band first, then the straps |
From a fitting guide by Brava Lingerie, a retailer (opened October 22, 2026). Brands cut differently, so a size that passes these checks in one brand can fail them in another. Try the calculator’s size first, then use these checks to move from it.
Methodology
Band = the snug underbust in inches, rounded to the nearest even number; an odd whole inch takes the smaller band. Cup = bust minus band, rounded to a whole inch, one letter per inch. Centimeters are converted at 2.54 cm to the inch, and the result is the same whichever unit you type in. The European figure is the centimeter band for the underbust and nothing more. The chart covers an underbust of 24 to 57 in and a bust up to 9 in larger than the band.
How to use this tool
- Choose inches or centimeters.
- Measure tightly around the ribcage just below the bust and enter it as the underbust.
- Measure loosely around the fullest part of the bust and enter it.
- Read the US and UK size, the European band, how the size was worked out and the sister sizes.
Frequently asked questions
- How do I measure my bra size at home?
- Take two measurements with a soft tape, in inches or centimeters. The underbust goes tightly around the ribcage just below the bust, with the tape level. The bust goes around the fullest part. Enter both and the page gives the band, the cup and how each was worked out.
- What is my bra size with a 34 inch underbust and a 38 inch bust?
- 34D in US and UK sizing. The band is 34 and the bust is 4 in larger, which is a D. The sister sizes are 36C and 32DD/E (32DD in UK lettering), and the European band is 85.
- What are sister sizes?
- Sizes with the same cup volume on a different band: one band up with one cup down, or one band down with one cup up. For 34C they are 36B and 32D. They are the sizes to try when the cup fits and the band does not.
- Why is the European size only a band number?
- European cups follow a different rule. The band is the centimeter size for the underbust: 83 to 87 cm is an 85. The cup is one letter per 2 cm of difference between the bust and a loosely measured underbust, starting at AA for 10 to 12 cm, and brands apply it differently. The page lists that cup table for reference and leaves the letter to the brand’s chart.
- Why does a size chart say US 34 is EU 75 when this page says 85?
- The two answer different questions. This page reads the band from your underbust: 34 in is about 86 cm, which is an EU 85. Conversion charts pair labels, and some US labels sit 4 above the underbust, so a US 34 label can belong to a 30 in underbust, which is an EU 75. If the brand you are buying from prints a conversion chart, follow it.
- Should I add 4 inches to my underbust for the band size?
- Not with this calculator. It uses the underbust itself, rounded to the nearest even inch, as the band. The older plus-four method adds 4 to an even underbust or 5 to an odd one, so a 34 in underbust becomes a 38 band and the cup letter drops to match. British brands use the underbust as the band, and Wikipedia notes the US retailer Kohl’s switching from plus-four to the underbust between 2013 and 2018.
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