Cup Size Calculator - Convert UK, USA & EU Bra Sizes Instantly

Cup Size Calculator – Convert UK, USA & EU Bra Sizes Instantly | International Converter

  • Adam
  • November 5, 2025

Convert your bra cup size between UK, USA, and European sizing systems instantly. Free cup size calculator with comprehensive conversion charts. Understand international bra size differences for confident online shopping.

Cup Size Calculator - Convert Between UK, USA & EU Sizes

Confused about international bra cup size conversions? This free cup size calculator instantly converts your cup size between the United Kingdom, United States, and European sizing systems. Select your current size system and cup letter to discover equivalent sizes across all three international standards. Perfect for online shopping, international travel, or understanding sizing differences when purchasing from global retailers.

Convert Your Cup Size

Your Cup Size Conversions

## Understanding Cup Size Differences Across Systems

Cup sizes vary significantly between international sizing systems. The primary reason for these differences lies in how band sizes are calculated. Since cup size represents the difference between your bust and underbust measurements, different band size methodologies result in different cup letter progressions across countries.

The UK sizing system uses actual underbust measurements rounded to even numbers, resulting in a specific cup progression. The USA sizing system adds four or five inches to the underbust measurement (the plus-four method), which shifts the cup sizes differently. The European system uses centimeter-based metric measurements, creating yet another cup progression pattern.

## Complete Cup Size Conversion Chart
Measurement DifferenceUK CupUSA CupEU CupTypical Breast Volume
Less than 1 inch / Less than 11 cmAAAAAAVery Small
1 inch / 11-12 cmAAASmall
2 inches / 13-14 cmBBBSmall to Medium
3 inches / 15-16 cmCCCMedium
4 inches / 17-18 cmDDDMedium to Large
5 inches / 19-20 cmDDDDELarge
6 inches / 21-22 cmEDDDFLarge
7 inches / 23-24 cmFDDDD/GGExtra Large
8 inches / 25-26 cmFFHHExtra Large
9 inches / 27-28 cmGIIExtra Extra Large
10 inches / 29-30 cmGGJJVery Large
11 inches / 31-32 cmHKKVery Large
12 inches / 33-34 cmHHLLExtremely Large
13 inches / 35-36 cmJMMExtremely Large
14 inches / 37-38 cmJJNNExtra Extremely Large
15 inches / 39-40 cmKOOExtra Extremely Large
## Why Cup Sizes Are Not Universal

UK Cup Sizing

Progression: AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K, KK, L

Each Step: 1 inch difference

Band Calculation: Actual underbust rounded to even numbers

Result: Band sizes affect cup progression uniquely in UK system

USA Cup Sizing

Progression: AA, A, B, C, D, DD, DDD, DDDD, H, I, J, K, L, M, N, O

Each Step: 1 inch difference

Band Calculation: Underbust + 4 inches (even) or + 5 inches (odd)

Result: Plus-method shifts cup sizing compared to UK

EU Cup Sizing

Progression: AA, A, B, C, D, E, F, G, H, I, J, K, L, M, N, O

Each Step: 2 centimeters difference

Band Calculation: Actual underbust in 5 cm intervals

Result: Metric system with consistent progression

## Key Conversion Points to Remember

Critical Point: While USA and UK have similar cup letter sequences in smaller sizes, they diverge significantly at DD and beyond. A UK DD is equivalent to a USA DD but a UK E is equivalent to a USA DDD. Always verify your size when shopping internationally, as different sizing systems create different cup volumes at the same letter designation.

  • AA Through D Cups: UK, USA, and EU systems are relatively aligned in their first letters. However, USA band sizes differ from UK due to the plus-four method, so complete size conversions require checking both band and cup.
  • DD and Larger Cups: Cup sizes begin to diverge significantly. UK DD equals USA DD and EU E. This means a UK 34DD is NOT the same as a USA 34DD because the band calculation method differs, even though the letters align.
  • Alternative Notations: USA sometimes uses DDD instead of E, DDDD instead of F or G. EU strictly uses single letters throughout. UK uses double letters (DD, FF, GG, HH, JJ, KK) for larger sizes.
  • Metric vs Imperial: UK and USA use inches for measurement calculations. EU uses centimeters. Understanding the measurement basis helps explain why cup sizes differ despite seeming to use similar letters.
  • Band Size Impact: Cup size is calculated as the difference between bust and band measurements. Different band calculation methods mean different final cup letters for the same actual bust measurements.
## Detailed Conversion Examples
If You WearEquivalent UK SizeEquivalent USA SizeEquivalent EU Size
34A UK34A34AA75A
34B UK34B34A75B
34C UK34C34B75C
34D UK34D34C75D
34DD UK34DD34D75E
34E UK34E34DD75F
36D UK36D36C80D
36DD UK36DD36D80E
36E UK36E36DD80F
## Why Shopping Internationally Requires Careful Conversion

When shopping for bras online from international retailers, simply matching cup letters can lead to purchasing the wrong size. For example, if you normally wear a US 34D, you might assume a UK 34D from a British retailer is the same size. However, a UK 34D is actually equivalent to a US 34C, not 34D, because the USA uses the plus-four method while the UK uses actual measurements.

Many online retailers now provide size conversion charts, but these charts sometimes contain errors or oversimplifications. Understanding the underlying calculation methods helps you verify conversions and make confident international purchases.

## How to Convert Your Cup Size Manually

Manual Conversion Steps

Step 1: Know your actual underbust and bust measurements
Step 2: Calculate measurement difference in your measurement unit
Step 3: Reference the measurement difference in conversion charts
Step 4: Identify equivalent cup letter in target system
Step 5: Verify by cross-referencing band size calculations

The most accurate conversion method involves understanding your actual measurements rather than simply converting cup letters. If you measure 33 inches underbust and 38 inches bust, your measurement difference is 5 inches. In the UK system, this equals DD cup. In the USA system with plus-four method (37 band size, so measurement difference is 38-37=1 inch), this would be A cup—completely different despite potentially being called "DD" or "A" respectively.

## Frequently Asked Questions
Why is my cup size different when I shop internationally?
Different countries use different band size calculation methods. Since cup size is determined by the difference between bust and band measurements, different band calculations result in different cup letters for the same actual breast volume. USA adds to underbust (plus-four), UK uses actual measurement, and EU uses metric in 5 cm intervals. Always verify the complete size, not just cup letters.
Is a UK DD the same as a USA DD?
No, UK DD and USA DD are not the same, even though they use the same letter. Because USA band sizes are calculated differently (plus-four method), the complete size differs. A UK 34DD is equivalent to a USA 36C or 34D depending on the actual measurements, not a USA 34DD. Always check both band and cup when converting.
How do I know which system a retailer is using?
Most retailers clearly indicate their sizing system, typically showing it alongside their size charts. Common labels are "UK sizing," "US sizing," "International," "European," "EU," or specific country names. If unclear, check the retailer's size conversion chart or contact their customer service. Many retailers now offer multiple size systems on their website for convenience.
Can I use the same cup size converter for all band sizes?
Cup size conversions are consistent across band sizes within the same systems. A UK C is always equivalent to a USA B and EU C, regardless of whether your band is 30, 34, or 38. The conversion relationship between sizing systems remains proportional across all band sizes.
What about other countries like Australia or France?
Australia uses UK sizing for band sizes but their cup sizing follows UK progression. France has its own system using similar measurements to EU but sometimes with different notations. Canada typically uses USA sizing. When shopping internationally, identify which of the three main systems (UK, USA, or EU) the retailer uses, as most countries follow one of these standards.
Why does my band size also change in conversions?
Band sizes between systems are identical numerically (28-44), but they represent different measurements due to different calculation methods. A UK size 34 represents your actual 34-inch underbust. A USA 34 represents a 30-inch underbust (30+4=34). An EU size 75 represents an 75 cm underbust. So while numbers are similar, they correspond to different actual measurements across systems.
Should I get professionally fitted before using this converter?
Professional fitting is recommended as it establishes your accurate base size in one system. Once you know your size in one system, this converter helps you find equivalents in others. However, understanding your actual bust and underbust measurements is more valuable than just knowing a letter size, as it lets you verify any conversion.
How accurate is cup size conversion?
Cup size conversion is quite accurate when based on measurement differences rather than just letter matching. However, individual bra brands and styles fit differently regardless of size. What matters most is your actual measurement difference (how many inches or centimeters between underbust and bust), as this determines your true cup volume across all systems.

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