This guide explains why the same C cup can fit differently around the world and how to convert your size so you can shop globally with confidence.
The same C cup can hug you perfectly in one country and dig in or gape in another because different sizing systems use different band measurements, cup steps, and letter rules, and individual brands layer their own quirks on top. Once you understand how those systems translate, you can convert your size, ignore the label drama, and shop anywhere without blaming your body.
Ever slipped into your “usual” C cup on vacation, looked in the mirror, and thought, “Who shrunk my boobs or stretched this bra?” One well‑fitting bra can legitimately be tagged 34C, 75C, 90C, or 12C depending on where it’s sold, even though your body never changed. This guide shows why those standards clash, how to turn your real measurements into a global size, and how to pick affordable, romantic lingerie that actually fits instead of playing dressing‑room roulette.
How Bra Sizes Are Supposed To Work (And Where It Goes Sideways)
Bra sizing starts with two pieces of information: a band number that reflects the measurement around your ribcage and a cup letter that reflects breast volume based on the difference between your full‑bust and band measurements. Brands like Glamorise spell this out clearly and show how the band number comes from a snug measurement around the chest with cups built from the bust‑minus‑band difference. Glamorise also reminds you that as band size goes up, cup letters represent different actual volumes, so a 34D and a 40D are not the same amount of breast tissue.
Most systems agree on the basics: the band is the numeric part of your size, and the cup is determined by how many “steps” separate your bust from your band. The trouble starts because US and UK systems increase cups in 1‑inch steps, while many European systems increase cups every 2 centimeters (about 0.8 inches). Because those step sizes are different, they never line up perfectly. The overview at BustyResources shows that UK and US cups climb one letter for each inch of bust–band difference, but EU and similar systems climb per 2‑centimeter (about 0.8‑inch) increments and label bands directly in centimeters, so discrepancies grow with every size jump.
Regional systems also label bands differently. In much of Europe, your band is essentially your snug underbust measurement in centimeters rounded to the nearest 5; a torso around 29.5–30.5 inches (about 75 centimeters) usually lands in an EU 75 band, which conversion charts from BraForMe and AmpleBosom equate with a UK/US 34. France and Spain often use “BEF” style bands that are 15 higher than the EU number, so that same bra can be labeled 75C in the EU chart and 90C in France while fitting the same ribcage. Primadonna’s explanation of EU and French bands underlines this fixed 15‑point offset.
Then brands add their own quirks. There is no global rule for how tight a band must be, so two bras marked with the same band number can feel very different. Industry fitters explain that some brands cut softer, stretchier bands that feel loose, while others use firmer fabrics and snug cuts that feel tighter even on the same numeric size. BraFittingsByCourt’s comparison of US and UK sizing and plus‑size specialists like AmpleBosom both stress that the band fit can vary significantly by brand, especially in fuller‑bust and plus‑size ranges.
Add one more twist: cup volume is relative to the band. A 34C has less cup volume than a 38C, even though the letter matches, because the 38 band is bigger to begin with. Glamorise explicitly notes that the same letter on different bands does not represent the same volume, which is why a 34D and a 38D are completely different bras on the body. Glamorise and multiple fit guides warn that chasing a letter without checking band size is a fast track to spillage, gaping, or sore shoulders.
The Big Systems: US/UK vs EU/FR vs AU
US and UK: Same Numbers, Messy Letters
US and UK systems both use inches for bands and the same 1‑inch cup step, so in theory they should be easy to translate. In practice, they fight over letters. US brands often go D, DD, DDD, then jump to F, G, and beyond, with some skipping or renaming letters so that a DD might also be labeled E and a DDD might be labeled F depending on the manufacturer. BraFittingsByCourt’s breakdown points out that this chaos really hits from DD upward.
The UK system leans into double letters: D, DD, E, F, FF, G, GG, H, HH, J, and onward, which makes the internal step pattern more consistent but creates huge confusion when you cross the Atlantic. That same article notes that a UK H cup is roughly three cup sizes larger in volume than a US H, so treating those letters as equivalent can shove you into a bra that is dramatically too big or too small.
Some US and European brands quietly use UK cup logic on US tags, so you cannot assume that every “F” or “H” you see follows one rule.
Because cup letters are so unreliable above D, some retailers use a neutral code. HerRoom’s Universal Cup Sizing system maps cups onto D‑based numbers: their D3 corresponds to a US DDD, a UK E, and a European F, letting you ignore the letter soup and follow the D‑number instead. That kind of cross‑mapping is exactly what proves that “C cup,” “E cup,” or “H cup” mean nothing without context.
Europe and France: Everything in Centimeters
European (EU) bra sizing writes bands in centimeters. Guides from BraForMe and Floret’s conversion overview show that if your underbust is around 30 inches (about 76 centimeters), you will typically land in an EU 75 or 80 band, with cups that step up every 2 centimeters (about 0.8 inches) of bust–band difference. Those same guides illustrate that a US 34B becomes roughly an EU 75B, a 36C becomes an 80C, and a 38D becomes an 85D once you rewrite the band in centimeters.
France, Spain, and some neighboring countries use BEF‑style systems that bump the band number 15 points higher than the EU label while keeping the cup letter the same. That means EU 75C and FR 90C can be hanging next to each other on a rack and fit the same body, even though 90 looks like a much “bigger” size. Both BustyResources and Primadonna emphasize that these differences are formatting, not body changes.
Australia and “International” Labels
Australia and New Zealand borrow from both dress sizes and bra sizes. Many Australian bands are labeled 8, 10, 12, 14, and so on, with 8 roughly corresponding to a US 30, 10 to a 32, and 12 to a 34, while cups often follow a mix of UK and EU letters. Conversion charts from AmpleBosom confirm that a UK 32 band maps to an AU 10 and a UK 34 to an AU 12, and that bands convert in similar two‑step jumps to EU and French numbers.
Retailers that sell globally often add yet another label called “International” or “INT,” where the band is written in the centimeter‑style EU number but sits next to US and UK tags on the same hanger. Sites like Lingerie Room’s international chart explanation and the conversion tables at MsPomelo lean on this shared “international” column to help shoppers bounce between AU, UK, US, and EU labels.
The bottom line: if your C cup suddenly looks like a 12C, 75C, or 90C, that is not your boobs changing overnight; it is the band language switching from inches to centimeters to dress‑style numbers.
How To Build Your Own “Master Size” Before You Shop Globally
Before you get lost in charts, start with your body, not the tag on your oldest bra. At home, take two measurements with a soft tape: first, measure snugly around your ribcage directly under the bust, keeping the tape parallel to the floor; then measure around the fullest part of your bust, relaxed, without squashing tissue. Brands like Supporting Eve base their global calculators entirely on these two numbers and present the size as a starting point instead of a decree, explicitly telling you to prioritize comfort over the output. Supporting Eve’s global size calculator and BraForMe’s bra size chart and calculator both use this method.
Once you have your two measurements, the difference between bust and band places you in a cup scale. In inch‑based systems, each inch of difference moves you up one cup step, so a 3‑inch gap is roughly a C, a 4‑inch gap a D, a 5‑inch gap a DD/E, and a 6‑inch gap somewhere around a DDD/F depending on the brand’s letter scheme. HerRoom’s Universal Cup Sizing explanation illustrates that their D3 cup corresponds to a US DDD, a UK E, and a European F, so one real‑world body with a 6‑inch difference can show up under three different letters in three different regions.
To sanity‑check your “master size,” use both measurement and mirror. Vogue’s practical fit guidance suggests putting on the bra, adjusting straps, and doing a 360‑degree check: raise your arms, bend, twist, and pop on a fitted T‑shirt. If the band rides up, the center gore floats away from your sternum, cups cut in or spill over, or straps are doing all the lifting, the size is off, no matter what the tape measure said. Vogue’s bra measuring guide and HerRoom’s fitting advice agree that the band should stay level, the cups should fully hold your tissue, and the straps should merely fine‑tune support, not act like suspension cables. HerRoom even notes that about half of women blaming “narrow shoulders” for strap slip are really dealing with bands that are one or two sizes too big.
When your base size feels solid in one brand, use conversion charts as a translation tool, not a verdict. Sites like Lingerie Room, AmpleBosom, BraForMe, and MsPomelo all treat their charts as guides only and highlight that brand‑to‑brand variation is real. Think of the chart as your translator: it gets you into the right neighborhood, then your body decides which house you actually move into.
Double Letters, Sister Sizes, And Why C Cups Aren’t Created Equal
Those double letters and mysterious “sister sizes” are not just lingerie folklore; they are the key to surviving international sizing without tears. UK brands use a full set of doubles—DD, FF, GG, HH, JJ, and so on—to represent every 1‑inch jump in cup volume, while many US brands write that same volume as D, DD, DDD, F, or G depending on their internal scheme. BraFittingsByCourt shows how that plays out in the wild and highlights the infamous example where a UK H cup is about three cup sizes larger than a US H.
Sister sizes explain why one C cup can be a dream in one band and a disaster in another. Because cup volume is tied to band size, going down one band size and up one cup size usually preserves roughly the same volume; for example, 34C, 32D, and 36B sit in the same ballpark for cup capacity but change how tight the band feels. Both HerRoom’s fitting room and Glamorise’s size explainer highlight this band‑cup trade as a practical way to tweak fit when the band is slightly too loose or snug but the cup volume feels right. Glamorise also reinforces that a correctly fitting band should allow only one or two fingers underneath and should provide most of the support while cups simply contain breast tissue smoothly. Glamorise spells out how wearing too big a band or too small a cup ruins that balance.
Now layer conversions onto sister sizes. If a 34C in one brand is perfect but the band rides up on date‑night lingerie from another brand, you might drop to a 32D for more support. That 32D can show up on international charts as an EU 70D and a French 85D, and on some Australian tags as a 10D, based on mappings shared by Floret and AmpleBosom. The cup is still roughly your “C‑ish” volume, but the label now wears a different band number and sometimes even a different letter, depending on which country’s logic the brand follows.
One Bust, Many Labels: A Quick Comparison
To see how wild this gets, take one well‑fitting bra and watch it travel. Imagine a bra that fits like a classic C cup on a 34‑inch band in a UK brand. Conversion tables from AmpleBosom, BraForMe, and Floret collectively show how that same physical bra is typically labeled across systems.
System |
Example label |
What it really means |
US / UK |
34C |
Inch‑based band around a 34‑inch ribcage; C is about a 3‑inch bust–band difference. |
EU (most of Europe) |
75C |
Band written as an underbust of about 29.5 inches (about 75 centimeters), same volume. |
France / Spain |
90C |
Same fit as EU 75C, but band number bumped 15 points higher; cup letter unchanged. |
Australia / NZ |
12C |
Band written in dress‑style numbers; 12 aligns roughly with a UK/US 34 band. |
Nothing about your chest changed between 34C, 75C, 90C, and 12C; only the language on the tag did.
And if that same bra were cut by a US brand that prefers single letters over doubles, there is a good chance the equivalent one size up or down might be labeled D or B, depending on their internal chart. This is why obsessing over being a “C cup” is a losing game; what matters is which combination of band and cup gives you the lift, comfort, and silhouette you want.
Shopping Smart For Affordable, Romantic Lingerie Across Borders
When you are hunting for an affordable set that looks great under candlelight and still feels good at 2:00 AM, treat sizing as part science and part styling tool. Start with your best‑fitting everyday bra, confirm that it actually fits using the mirror tests from Vogue’s bra fit advice, then use international charts from places like Lingerie Room, AmpleBosom, or MsPomelo to translate that size into the system used by whichever lacy balconette or strappy longline has caught your eye.
On the body, your checklist stays the same whether the tag reads 34C or 75D. The band should sit level and snug without digging, the center front should sit close to your sternum (unless you are in a plunge cut by design), and cups should contain all your tissue with no “quad‑boob” or empty space. HerRoom reminds you that the band provides most of the support, straps only fine‑tune it, and a bra that falls down when you slip the straps off is a band problem, not a shoulder problem. HerRoom’s strap and support research backs this up with data from hundreds of thousands of women.
For romantic occasions, you can absolutely prioritize pretty details without sacrificing fit. Once you know your master size and a couple of sister sizes, you can hunt down sales and budget‑friendly lines in those ranges instead of rebuying the same missized 34B forever. If a delicate lace demi from a European brand only comes in 75D and you usually wear a supportive 34C T‑shirt bra, you can confidently try that 75D knowing the band and cup are in your natural neighborhood and then tweak with sister sizes if needed. Charts from BraForMe and Floret make those cross‑system hops far less risky.
Re‑measure at least once a year and after any big life shifts like weight changes, pregnancy, or hormone swings, because your “master size” can drift even if you stay in the same country. Multiple fit guides, from Glamorise to Supporting Eve, emphasize treating calculators and charts as starting points, not commandments. The real win is a bra that supports you, lets you breathe, and makes you feel like the main character, regardless of whether the label says 34C, 75D, or something that looks “bigger” than you expected.
FAQ: Fast Answers For The Fitting Room
Why does my size look huge or tiny abroad?
Band numbers and cup letters are formatted differently by region, so French and Spanish bands are routinely 15 points higher than their EU equivalents and Australian bands often use dress‑style numbers like 10 or 12 instead of 32 or 34. Conversion overviews from BustyResources and AmpleBosom show that these “big” numbers often represent the exact same ribcage measurement you already have.
Is there any truly universal bra size system?
Not yet, but tools exist to get close. International charts from BraForMe, MsPomelo, and HerRoom’s Universal Cup Sizing give you a consistent size “language” that works across many brands, even though the tags themselves still differ.
What if I fall between sizes when I measure?
Round to the nearest comfortable band, then use sister sizes to explore: if the band feels loose, go down one band and up one cup; if it feels too tight, go up one band and down one cup while watching the fit cues. Fit‑focused guides such as those from Vogue and Glamorise echo that the mirror and your comfort trump the exact number the tape spits out.
Your curves are not inconsistent; the sizing systems are.
Once you stop worshiping the letter on the tag and start using your measurements, sister sizes, and a few solid conversion charts, you can flirt with any brand, in any country, and still walk away in lingerie that supports you, flatters you, and feels as romantic as it looks.
