Bra Size Calculator
Measure your underbust and bust to find your bra size, or convert a size you already wear between US, UK, EU, French and Australian sizing, with sister sizes for a better fit.
Sister sizes
Same cup volume on a different band. Go up a band and down a cup if the band is tight, or down a band and up a cup if it rides up.
Cup size conversion
Conversions are approximate. Sizing varies between brands and styles (especially for US cups above DD), so treat the result as a starting point and check the fit.
How to use the Bra Size Calculator
- Measure your underbust snugly around your ribcage, right under your bust, keeping the tape level.
- Measure your bust loosely around the fullest part while wearing a non-padded bra.
- Enter both measurements, choose inches or cm and press Calculate.
- Read your size in every region and check the sister sizes if the band or cup does not fit.
- Already know your size? Use the converter tab to translate it to another country's sizing.
How the bra size calculation works
A bra size has two parts: the band (the number) and the cup (the letter).
- Band: measure snugly around your ribcage directly under your bust, in inches. Round to the nearest whole inch, and if it is odd, round up to the next even number. With the traditional method you add 4 inches to an even measurement or 5 to an odd one.
- Bust: measure loosely around the fullest part of your bust, keeping the tape parallel to the floor, and round to the nearest inch.
- Cup: subtract the band from the bust. Each inch of difference is one cup size: 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD.
Worked example: underbust 31.5 in rounds to 32 (even), so the band is 32. The bust is 37 in. 37 − 32 = 5 in, which is a DD cup, so the size is 32DD (UK 32DD, EU 70E, FR 85E, AU 10DD).
Band size conversion chart
| US / UK | EU | FR / BE / ES | AU / NZ | Underbust (in) | Underbust (cm) |
|---|---|---|---|---|---|
| 28 | 60 | 75 | 6 | 27–28 | 58–62 |
| 30 | 65 | 80 | 8 | 29–30 | 63–67 |
| 32 | 70 | 85 | 10 | 31–32 | 68–72 |
| 34 | 75 | 90 | 12 | 33–34 | 73–77 |
| 36 | 80 | 95 | 14 | 35–36 | 78–82 |
| 38 | 85 | 100 | 16 | 37–38 | 83–87 |
| 40 | 90 | 105 | 18 | 39–40 | 88–92 |
| 42 | 95 | 110 | 20 | 41–42 | 93–97 |
| 44 | 100 | 115 | 22 | 43–44 | 98–102 |
Signs your bra does not fit
- Band rides up at the back: the band is too big. Go down a band and up a cup (34C → 32D).
- Band digs in or feels tight: try the next band up and a cup down (34C → 36B).
- Gaps at the top of the cup: the cup may be too big, or the style may not suit your shape.
- Spilling over the cup or wire sitting on breast tissue: go up a cup size.
- Straps slip or carry the weight: most support should come from the band, so it is probably too loose.
A new bra should fit on the loosest hook, so you can tighten it as the elastic stretches over time.
Frequently asked questions
How do I calculate my bra size?
Your band size is your underbust measurement in inches, rounded to the nearest even number. Your cup size is the difference between your bust and band measurements: 1 inch is an A, 2 inches a B, 3 a C, 4 a D, 5 a DD and so on.
What are sister sizes?
Sister sizes have the same cup volume on a different band. Going up one band size and down one cup (for example 34C to 36B) keeps roughly the same cup volume, which helps when the cups fit but the band is too tight or loose.
How do UK and US bra sizes differ?
Band sizes are the same in the US and UK. Cups match up to DD, then they differ: after DD the UK goes E, F, FF, G, GG, while US brands usually use DDD (or F), G, H, I. A UK 34F is about a US 34G.
How do EU and French bra sizes work?
EU band sizes are in centimeters in steps of 5, so a 34 band is an EU 75. French bands are 15 higher than EU bands (FR 90 = EU 75). EU and French cups go A, B, C, D, E, F, G without doubled letters.
Should I add 4 inches to my band measurement?
The traditional +4 method was used when bras were less stretchy, and it often produces a band that is too big. Most fitters today use the snug underbust measurement. This calculator offers both methods so you can compare.
Is the result exact?
No calculator is exact because breast shape, bra style and brands differ. Use the result as a starting point and try sister sizes. A professional fitting is the most reliable.