Bra Size Calculator
Enter your underbust and overbust measurements to find your exact bra size — in US, UK, EU, FR, AU, JP or KR sizing — with sister sizes, fit tips, and international conversions.
A bra size calculator works by comparing two measurements: your underbust (snug measurement directly under the bust) and your overbust (loose measurement at the fullest point of the chest). The difference between the two measurements determines your cup size, while the underbust rounded to the nearest even number determines your band size. A 34DD, for example, means a 34-inch band and a 5-inch bust-to-band difference.
Are bra size calculators reliable?
A bra size calculator is reliable when it uses clear underbust and overbust measurements, explains the sizing system being used, and treats the result as a starting size rather than a final guarantee. The calculator gives your best mathematical size, while the final fit still depends on brand shape, cup depth, band stretch and breast tissue distribution.
The most accurate online bra size calculators ask for at least two measurements: a snug underbust and a loose full-bust measurement. They are useful for larger cup sizes too, but full-bust results should be checked with fit signs such as a flat center gore, no cup spillage, a level band and underwires sitting around—not on—breast tissue.
| Question | Short answer | What to check next |
|---|---|---|
| Are calculators accurate for larger cup sizes? | Yes, if measurements are taken carefully and the calculator includes extended cup logic. | Check cup depth, wire width, gore position and side containment. |
| What makes an online calculator accurate? | It uses raw measurements, supports inches and cm, explains cup difference and shows sister sizes. | Avoid tools that only ask for dress size, weight or vague body type. |
| What measurements do I need? | Snug underbust and loose overbust are the minimum. A leaning bust can help for projected or soft tissue. | Measure three times and use the most consistent reading. |
| Should the result match every brand? | No. The result is your starting size, not a universal brand guarantee. | Use fit symptoms and sister sizing when trying a new brand. |
Large cup sizes: why the calculator is a starting point
For DD+ and extended cup sizes, a calculator is still helpful because it identifies the correct band-to-bust difference. The challenge is that larger cup sizes are more affected by projection, root width, tissue softness and brand construction. Two people can both calculate as 34G, but one may need a narrow projected cup while the other needs a wider full-cup style.
If your calculated size is above DD/E, use the number as your first try-on size, then confirm it with fit checks: the center gore should lie flat, the band should stay level, the wires should surround the breast tissue, and the cup edge should not cut in. If the cup volume feels right but the band feels wrong, use the sister size shown by the calculator.
What are the most accurate online bra size calculators?
The most accurate online bra size calculators are measurement-based tools that show their logic clearly. A good calculator should accept inches and centimetres, calculate the band and cup separately, support US/UK/EU conversions, show sister sizes and explain why the result may vary by brand. A less reliable calculator may give one size without explaining how it was calculated.
How to measure for the most accurate result
Two measurements are all you need. The accuracy of your result depends entirely on how well you take them. Here’s the exact method our calculator uses.
- Remove your bra. Measuring without a bra gives the most accurate underbust reading. If you must wear one, use a non-padded, well-fitting bra only.
- Measure your underbust. Wrap a soft tape measure directly under your bust, where your bra band sits. Keep it firm — snug, not cutting in. Exhale normally. Record this number in inches or centimetres (the calculator accepts both).
- Measure your overbust. Lean slightly forward and wrap the tape loosely around the fullest part of your chest. The tape should be straight across the back. Don’t compress the breast tissue — this measurement should be loose, not tight.
- Enter both numbers above. The calculator auto-detects inches vs centimetres (values over 60 are treated as cm). Select your preferred sizing system, then your result appears instantly.
- Try your result and adjust. If the band feels too tight, try the sister size with a larger band (+2 inches) and smaller cup. If it feels loose, try the smaller band (-2 inches) with a larger cup. Both alternatives maintain the same cup volume.
How bra sizes actually work
The bra size system confuses most people because it looks like two separate measurements but is really one combined proportional formula. Understanding it removes the guesswork.
Band size
Your band size is derived from your underbust measurement, rounded to the nearest even number (US/UK add 4 inches; EU rounds to the nearest 5cm; FR adds 15 to that). The band provides 80% of a bra’s support — not the straps. If your band feels loose on the tightest hook when new, you need a smaller band.
Cup size
Cup size is not an absolute volume — it’s the difference between your overbust and band size. A D cup on a 32 band contains far less volume than a D cup on a 40 band. This is why cup letters alone are meaningless without the band number, and why sister sizes exist.
| Difference (inches) | US / UK Cup | EU Cup | FR / BE Cup | Volume description |
|---|---|---|---|---|
| ≤ 1 in | AA | AA | AA | Very small — minimal projection |
| 1 in | A | A | A | Small — modest projection |
| 2 in | B | B | B | Moderate — average for smaller frames |
| 3 in | C | C | C | Average — most common cup in the US |
| 4 in | D | D | D | Full — well above average volume |
| 5 in | DD / E | E | E | Very full — common in specialty sizing |
| 6 in | DDD / F | F | F | Large — requires structured support |
| 7 in | G | G | G | Very large — full-bust specialist brands |
| 8 in | H | H | H | Extended — Freya, Elomi, Panache territory |
How bra cup sizes actually work
Bra cup sizes are proportional, not fixed. A cup letter only has meaning when it is paired with a band number. This is why 32D, 34D and 40D are not the same cup volume even though they all use the letter D. As the band increases, the same cup letter holds more volume.
The simple rule is: cup size = bust measurement minus band size. About 1 inch of difference is usually an A cup, 2 inches is a B cup, 3 inches is a C cup, 4 inches is a D cup, and so on. This is also why sister sizes work: 34DD and 36D have similar cup volume, but the band tension is different.
| Common myth | Correct explanation |
|---|---|
| “D cup means large.” | D only means a 4-inch bust-to-band difference. A 30D is much smaller in volume than a 40D. |
| “Cup letters are universal.” | Cup letters change by country and brand, especially after DD/E. |
| “If the cup gaps, always size down.” | Gaping can also mean the cup shape is wrong, the band is too loose or the straps are overtightened. |
| “If the band is tight, go up one cup.” | Band tightness is usually fixed with a sister size, not by changing cup volume randomly. |
Sister sizes: same cup volume, different fit
Sister sizes are the single most useful concept in bra fitting. When you go up one band size, you go down one cup letter — the cup volume stays identical. This lets you adjust the tightness of the band without changing the amount of space in the cup.
Use sister sizing when: a bra fits in the cup but the band is too tight (go up one band, down one cup) or too loose (go down one band, up one cup). The calculator shows you all three options in the result — your size plus both sister sizes.
| Your calculated size | Tighter band sister | Looser band sister | When to use sister size |
|---|---|---|---|
| 32C | 30D | 34B | Band feels too tight → try 34B |
| 34B | 32C | 36A | Band too loose → try 32C |
| 34D | 32DD | 36C | Cup fits but band rides up → try 32DD |
| 36DD | 34E | 38D | Cup gapes but band fits → try 34E |
| 38C | 36D | 40B | Band leaves marks → try 40B |
For your full sister size matrix, use the sister size calculator.
International bra sizing: US, UK, EU, FR, AU and beyond
The same physical bra is labelled differently depending on which country’s sizing system a brand uses. Buying from international retailers without knowing the conversion is one of the most common causes of ordering the wrong size.
What is the difference between US and UK bra sizing?
US and UK bra sizing usually use the same band numbers, but the cup letters separate after DD. This is the main reason a bra labelled 34G in the US may not match a 34G in the UK. Before buying from an international brand, always check whether the brand uses US or UK cup progression.
| Point of comparison | US sizing | UK sizing |
|---|---|---|
| Band numbers | Usually 28, 30, 32, 34, 36 and upward | Usually 28, 30, 32, 34, 36 and upward |
| Cup sequence after D | D, DD/E, DDD/F, G, H, I | D, DD, E, F, FF, G, GG |
| Most confusing point | DDD and F may be used for the same cup step | Double letters such as FF and GG are separate cup sizes |
| Best buying rule | Use when the retailer or brand states “US sizing” | Use for many full-bust UK brands such as Panache, Freya and Elomi |
How international bra size conversion charts work
International conversion charts translate the same body measurements into different label systems. The cup volume should stay comparable, but the label may change because countries use different band units and cup sequences. For example, a 34DD in US/UK sizing is commonly shown as 75E in EU sizing and 90E in French sizing.
Conversions are most reliable when the chart converts both parts of the size: the band and the cup step. Converting only the band or only the cup letter can create a wrong result, especially above DD/E.
| US / CA | UK / AU / NZ | EU / DE / NL | FR / BE / ES / IT | JP / KR |
|---|---|---|---|---|
| 32A | 32A | 70A | 85A | 70A |
| 34B | 34B | 75B | 90B | 75B |
| 34C | 34C | 75C | 90C | 75C |
| 34D | 34D | 75D | 90D | 75D |
| 34DD | 34DD | 75E | 90E | 75E |
| 34DDD / F | 34E | 75F | 90F | 75F |
| 36C | 36C | 80C | 95C | 80C |
| 36D | 36D | 80D | 95D | 80D |
| 38B | 38B | 85B | 100B | 85B |
The key difference: EU/FR bands add 15–16cm to the underbust, while US/UK use an inch-based addition. Cup letters mostly align except at DD+ where US says DDD and UK says E. For the complete conversion across all 22 countries, use the global bra size converter.
Common bra fit problems — and what they tell you about your size
Most women wearing the wrong bra size experience at least one of these six symptoms. Each one points to a specific sizing error — and a specific fix.
How can you tell if bra cups are too small?
Your bra cups are probably too small if breast tissue spills over the top, escapes at the sides, the underwire sits on breast tissue, or the center gore floats away from the chest. A cup that is too small can also make the band feel tighter than it really is because the breast tissue is pushing the bra forward.
| Sign | What it usually means | Best fix |
|---|---|---|
| Top spillage / quad-boob | Cup volume is too small or cup edge is too closed. | Try one cup size up, or a more open cup shape. |
| Side spillage | Cup is too narrow or too small. | Try a wider wire, side-support style or one cup up. |
| Floating center gore | Cups are too small, too shallow or not projected enough. | Try one cup up or a plunge/full-bust style. |
| Underwire on breast tissue | Cup does not fully contain the breast root. | Try a larger or wider cup. |
| Band feels tight but rides forward | Cups may be too small and stealing space from the band. | Test one cup up before increasing the band. |
Band rides up the back
The band is too large. It should stay parallel to the floor. Try going down one band size and up one cup letter (your sister size).
Read: Band rides up fix →Cup spillage / quad-boob
The cup is too small. Breast tissue is overflowing the top or sides. Go up one cup size — or two if spillage is significant.
Read: Spillage fix →Gaping cups
The cup is too large, or the cup shape doesn’t match your breast shape. Try going down one cup, or trying a different cup style (plunge vs full cup).
Read: Gaping fix →Underwire poking or digging
The underwire is either too narrow (cup too small) or sitting on breast tissue rather than under it. Usually a cup size up resolves this.
Read: Underwire fix →Straps digging in
The band is too loose — straps are compensating for lack of band support. Tighten the band first. If already on the tightest hook, go down one band size.
Read: Strap fix →Center gore not lying flat
The cups are too small, or you have close-set or projected breasts. Go up a cup size or try a plunge style with a lower gore height.
Read: Gore fix →Why do different brands fit differently in the same size?
Different brands fit differently because a bra size label describes measurements, not the exact shape of the cup. A 34D can feel different across brands because of band elasticity, cup depth, wire width, gore height, strap placement, fabric stretch and whether the cup is moulded, padded, seamed or unlined.
| Brand difference | How it changes fit | What to do |
|---|---|---|
| Band stretch | A stretchy 34 band may feel like a 36, while a firm 34 may feel tight. | Check reviews and try the sister size if the cup volume is right. |
| Cup depth | Shallow cups can spill on projected breasts even in the correct size. | Try seamed, balconette or full-bust styles for more depth. |
| Wire width | Narrow wires can poke side tissue; wide wires can sit too far back. | Match wire width to your breast root width. |
| Gore height | High gores may press on close-set breasts; low gores may not anchor very full cups. | Try plunge for close-set shapes and full-cup for more containment. |
| Cup material | Moulded cups keep one fixed shape; stretch lace adapts better to asymmetry. | Use stretch fabrics when one breast is slightly larger. |
This is why the calculator shows your main size and sister sizes. Treat your result as a size range: start with the calculated size, then adjust only when a clear fit symptom tells you what needs to change.
Once you have your size, filter Amazon by band, cup and style. We’ve curated the best-rated bras for every size range — from 28A to 48K — with verified reviews and fast delivery.
Shop bras on Amazon →Choosing the right bra style for your breast shape
Your bra size tells you which bra will fit. Your breast shape tells you which style will look and feel best. These are two different things — and most fitting guides only address one of them.
| Breast shape | Best bra styles | Styles to avoid |
|---|---|---|
| Round / full | T-shirt, plunge, balconette | Heavy padding (adds unwanted volume) |
| Projected / forward | Full cup, moulded T-shirt, side-support | Balconette (lifts but doesn’t contain) |
| Wide-set | Plunge (low centre gore), front-close | T-shirt bras with high centre gores |
| Close-set | Full cup, minimizer, side-support | Plunge (pushes tissue further inward) |
| East-west (splayed) | Balconette, push-up, angled cups | Soft cup (no redirection) |
| Pendulous / soft tissue | Full cup, underwire, longline, minimizer | Wireless only (insufficient lift) |
| Shallow / flat | Padded balconette, push-up, moulded cup | Unlined (cups don’t fill properly) |
| Tubular / constricted | Soft cup, stretch lace, no underwire | Rigid moulded cups (cause discomfort) |
Use the breast shape identifier to find your shape and get a personalized style recommendation.
Every tool and guide you need for perfect bra fit
Your bra size is the starting point. These tools complete the picture — every link below is a confirmed live page on this site.
Full sister size matrix for your bra — every adjacent combination in one view.
Find your cup size from your measurements with detailed volume guidance.
Diagnose what’s wrong with your current bra — with step-by-step fixes for each issue.
Interactive tool: answer 5 questions, get a personalized diagnosis and fix plan.
Convert your size between UK, US, EU, FR, AU and 17 other international systems.
Complete US, UK and EU bra size charts from 28AA to 50K in one reference page.
All bra and lingerie size charts for every major sizing system in one place.
Interactive size chart — find your size on a visual grid with measurement overlays.
Side-by-side cup size comparisons with visual volume guides and real-world references.
Frequently asked questions about bra sizing
Are bra size calculators reliable for larger cup sizes?
Yes, bra size calculators can be reliable for larger cup sizes when they use accurate underbust and overbust measurements and support extended cup progressions. For DD+ sizes, always confirm the result with fit signs: the center gore should lie flat, the band should stay level, the wires should not sit on breast tissue, and there should be no top or side spillage.
What measurements do I need to calculate bra size accurately?
You need a snug underbust measurement and a loose overbust measurement at the fullest part of the bust. For projected, soft or larger cup sizes, a leaning bust measurement can also help check whether the cup volume needs more depth. Measure with a soft tape, keep it level, and avoid compressing the breast tissue.
What is the difference between US and UK bra sizing?
US and UK bra sizing usually use the same band numbers, but the cup sequence changes after DD. US sizing often uses D, DD/E, DDD/F, G, H and I. UK sizing uses D, DD, E, F, FF, G and GG. This is why a US 34G is not always the same as a UK 34G.
How can I tell if my bra cups are too small?
Your cups are likely too small if breast tissue spills over the top or sides, the center gore floats away from your chest, the underwire sits on breast tissue, or the band feels tight because the cups are pushing forward. Try one cup size up first before increasing the band.
How do international bra size conversion charts work?
International bra size conversion charts translate the same body measurements into different country labels. A conversion must account for both band sizing and cup progression. For example, a 34DD in US/UK sizing is commonly shown as 75E in EU sizing and 90E in French sizing. Above DD/E, always check the brand’s stated sizing system.
Why do I measure differently every time?
Bra size measurements vary with posture, time of day, menstrual cycle phase, and tape tension. Measure in the morning before eating. Make sure the tape is level, you’re standing straight, and you exhale normally. Taking the measurement 3 times and using the average also reduces variation significantly.
Do I add 4 inches to my underbust?
The traditional “+4 inches” rule was developed when bras were made of less stretchy fabric. Modern bras are far more elastic, so most contemporary calculators (including this one) use the raw underbust measurement rounded to the nearest even number. Our calculator applies the correct formula for each sizing system automatically — you just need the raw measurement.
Why does my bra size vary between brands?
Brands cut bras differently. A 34C in one brand may fit like a 34D in another due to variations in cup depth, underwire width, band elasticity, and the specific block pattern used. This is why knowing your size range (e.g. 34C–34D or a 32D sister) is more useful than treating one number as absolute. Read reviews for fit notes when buying new brands.
What is a sister size and when should I use one?
A sister size is a bra that contains the same cup volume as your usual size but with a different band. Going up one band (e.g. 34C → 36B) gives the same cup volume with a looser band. Going down one band (34C → 32D) gives the same cup volume with a tighter band. Use sister sizes when the cup fits but the band doesn’t — rather than going up or down a cup size, which changes the volume.
Is a 34DD the same as a 34E?
It depends on the sizing system. In US sizing, DD and E are sometimes used interchangeably (both = 5 inches difference). In UK sizing, DD and E are different cups — E is one size larger than DD. In EU sizing, there is no DD; the sequence goes D → E → F. Our calculator shows your size in all 7 systems simultaneously so you never need to guess.
How often should I remeasure my bra size?
You should remeasure whenever your body changes significantly — weight gain or loss of 10+ pounds, pregnancy, post-partum, starting or stopping hormonal contraceptives, or menopause. For most people, an annual remeasure catches gradual drift. Bra size changes more frequently than most women realise: studies suggest the average woman’s size changes 6 times during her lifetime.
Can I use this calculator for a strapless bra?
Yes, but strapless bras typically require a band size that’s one tighter than your regular size, because all support comes from the band alone. If you calculate a 36C for regular bras, try a 34D (your sister size) for strapless. Use the sister size calculator to find your tighter-band equivalent quickly.
What if I’m between sizes?
If your measurements land exactly on a boundary, order both adjacent sizes where possible and do a wear test — or lean toward the larger cup with the smaller band, as it’s easier to adjust the band than to deal with a cup that’s too small. The calculator shows you sister sizes in the result panel for exactly this reason.
