Bra Size
Calculator
Enter two measurements to estimate a practical starting size across US, UK, EU, French and Australian systems—then check sister sizes and fit signs before you shop.
Need more than a quick estimate? Use the wider collection of fit, conversion and sizing tools at Bra-Calculator.com →
Measure to the nearest half inch. If between two numbers, note both.
Your bust should be larger than your underbust. If not, re-measure across the fullest point.
Full international conversion
| System | Band | Cup | Size |
|---|
Confirm the result with the full Bra-Calculator.com toolkit
Continue with dedicated sister-size, conversion, fit-problem and size-guide tools when you need more detail than this quick estimate.
Open Bra-Calculator.com →Fit before comparison
A celebrity’s reported size cannot calculate yours
Celebrity profiles can provide editorial sizing context, but they are not fitting templates. Two people with a similar bust measurement may wear different bra sizes because band measurement, breast shape, projection, tissue distribution, brand construction and personal comfort all matter.
Use your own measurements first. Then treat the result as a starting point and confirm it with the band, cup and underwire checks on this page.
Use my measurements →Step-by-step guide
How to measure for your bra size
A flexible tape measure, a mirror and two minutes. That’s all you need to get an accurate starting size.
A soft fabric or plastic tape measure — not a metal ruler. Measure in your underwear or a non-padded, unlined bra so the tape sits against your body, not a padded cup.
Underbust
Wrap the tape snugly — not tightly — around your ribcage, directly under your bust. Keep it level. Read while breathing normally. Round to the nearest whole inch.
Fullest bust
Wrap the tape across the fullest part of your chest — usually at nipple height. Keep it parallel to the floor. The tape should touch your skin but not compress it.
Note both numbers
Write both measurements down before you forget. If you’re between half-inch marks, note the range. The calculator uses both together — they’re meaningless in isolation.
Try the result
A calculated size is a starting point. Put the bra on and check the fit signs below. If something’s off, a sister size is usually the answer — same cup volume, different band.
The method explained
How bra size is actually calculated
Bra sizing uses two numbers — your underbust and the difference between underbust and bust — to produce a band and a cup estimate. Neither measurement is useful on its own. Together, they provide a sensible size to try first.
Band size
Your band size comes from your underbust measurement. US and UK bands are always even numbers. If your underbust is already even, that is your band. If odd, round to the nearest even — usually up. A 29-inch underbust gives a 30 band; 31 gives a 32.
This calculator uses a direct underbust method rather than automatically adding four inches. Modern elastic bands usually make that a more useful starting point, although individual brands may still fit tighter or looser.
Cup size
Subtract your underbust from your bust. The difference maps directly to a cup letter:
| Bust difference | US starting cup* | UK starting cup | EU starting cup |
|---|---|---|---|
| Less than 1 in | AA | AA | AA |
| 1 in | A | A | A |
| 2 in | B | B | B |
| 3 in | C | C | C |
| 4 in | D | D | D |
| 5 in | DD | DD | E |
| 6 in | DDD / F | E | F |
| 7 in | G | F | G |
| 8 in | H | FF | H |
| 9 in | I | G | I |
*US cup lettering varies by brand. Always check the retailer’s own chart, especially above D.
Your starting label combines the band and cup. For example, an estimated 30 band with a 4-inch difference begins at 30D.
Why the result is a starting point
Brands cut bands with different amounts of stretch. A 34 band in Freya fits differently from a 34 band in Victoria’s Secret. Wire shape, cup depth and gore height also vary. The calculated size is a structured place to begin, but trying the bra on and checking the fit remains the final proof.
Sister sizes explained
Same cup volume, different band
Sister sizes share the same cup volume while using a different band. Moving one band size up means moving one cup letter down — the total volume stays approximately the same.
Going up a band
If 32C feels too tight in the band, try 34B. Same cup volume, slightly looser band. Useful when you sit between band sizes.
Going down a band
If 34B feels too loose, try 32C. The cup holds the same volume but the firmer band gives more support — ideal for active wear.
Stock availability
Sister sizing can help when your exact label is unavailable. A 30D wearer may try 32C as a nearby option, then confirm the band and cup fit before buying.
| Band | AA | A | B | C | D | DD/E | DDD/F | G |
|---|---|---|---|---|---|---|---|---|
| 28 | 28AA | 28A | 28B | 28C | 28D | 28DD | 28DDD | 28G |
| 30 | 30AA | 30A | 30B | 30C | 30D | 30DD | 30DDD | 30G |
| 32 | 32AA | 32A | 32B | 32C | 32D | 32DD | 32DDD | 32G |
| 34 example | 34AA | 34A | 34B | 34C | 34D | 34DD | 34DDD | 34G |
| 36 | 36AA | 36A | 36B | 36C | 36D | 36DD | 36DDD | 36G |
| 38 | 38AA | 38A | 38B | 38C | 38D | 38DD | 38DDD | 38G |
| 40 | 40AA | 40A | 40B | 40C | 40D | 40DD | 40DDD | 40G |
Highlighted row is an example sister-size line, not a universal recommendation
Fit check guide
Signs your bra fits — and signs it doesn’t
A calculated size is only as accurate as the measurements behind it. The final proof is always how the bra sits on your body. Here’s what to look for.
Band is right when
- The band sits level around your body — not riding up at the back.
- You can slip two fingers under the band but not your whole hand.
- Raising your arms doesn’t pull the band away from your body.
- On a new bra, the loosest hook feels snug. You tighten as it stretches over time.
Cup is right when
- The underwire sits flat against your ribcage with no gaping or digging.
- The cup fully contains breast tissue — no spillage at top or sides.
- No wrinkling or buckling in the cup fabric.
- The centre gore lies flat against your sternum.
Common problems and fixes
- Band riding up: band too large. Go down a band, up a cup (sister size).
- Straps digging in: band too loose — it’s making straps compensate. Fix the band, not the straps.
- Breast spillage: cup too small. Go up a cup letter.
- Cup wrinkling: cup too large. Go down a cup letter.
- Underwire poking: cup too small or wire shape doesn’t suit your breast root — try the same size in a different brand.
Lean forward 45° and use your hand to gently scoop all breast tissue from under your arm into the cup before straightening up. Many apparent fit problems disappear when all tissue is correctly seated in the cup.
Frequently asked questions
Bra size questions, answered clearly.
How accurate is this bra size calculator?
This calculator uses a direct underbust method and the difference between your bust and underbust to estimate a starting size. The usefulness of the result depends on careful measurements, so measure twice and enter once.
Because brands differ in band stretch, cup depth and wire shape, trying the size on and checking the fit guide remains the final step.
Why do different bra calculators give different results?
The main reason is the band calculation method. Older calculators add 4–5 inches to the underbust before deriving the band (the “plus 4” method). This was developed when bra fabrics were stiffer. With modern elastic materials, it tends to produce oversized bands and undersized cups.
This calculator uses the snug method: your underbust is your band (rounded to the nearest even number). If you’ve always worn a 36B using the old method, the snug method may give you 32D — a different label for the same body.
Can I use a celebrity’s reported measurements to find my bra size?
No. Reported celebrity measurements are editorial reference information, not a fitting formula. Bra size depends on your own underbust, bust difference, breast shape, projection, brand and preferred firmness. Measure yourself and use the result as a starting size.
What is the difference between US, UK and EU bra sizes?
US and UK sizes share the same band numbers but diverge in cup letters above D. The UK system uses DD, E, F, FF, G, GG, H and so on. The US system uses DDD rather than E, and the progression differs beyond that.
EU sizing uses a different numbering system for the band: add approximately 15 to the US/UK band (so US 34 = EU 75). Cup letters are broadly similar at smaller sizes but diverge at larger ones. Australian sizing aligns closely with the UK system.
Should I measure in inches or centimetres?
Measure in whatever unit your tape measure shows clearly. This calculator accepts both. If you’re shopping for bras in the EU, measuring in centimetres may be useful because EU band sizes are expressed in centimetres (a 75 band = 75 cm). For US or UK shopping, inches are more practical.
Can my bra size change over time?
Yes, frequently. Weight changes, pregnancy, breastfeeding, hormonal shifts, age and changes in body composition all affect bra size. Many fitters recommend re-measuring every 6–12 months and whenever your usual bras start feeling different. Recalculate whenever something feels off.
What if my calculated size doesn’t feel right?
Start with sister sizes. If the band feels too tight, go up one band and down one cup (e.g. 32C → 34B). If it’s too loose, go the other way. If neither sister size works, the issue may be wire shape or cup construction rather than size — different brands suit different breast shapes at the same size. A specialist fitter can identify which shapes work for your body.
Continue exploring
Size guides, charts and directories
Editorial disclaimer: CelebrityBraSizes.com is an independent reference and is not affiliated with any brand or retailer. Calculated sizes are a starting point based on your measurements and the snug-method formula. Fit varies by brand, style and individual body shape. This content is informational and is not professional fitting or medical advice.