Bra Size Calculator UK : Find Your Perfect Fit in Minutes
Getting your bra size right makes a bigger difference than most people expect. The right fit means better posture, genuine comfort all day and no more straps digging in or bands riding up. Our free UK Bra Size Calculator gives you your size instantly, just enter two simple measurements and you're done.
How to Measure Your Bra Size at Home
All you need is a soft tape measure and two minutes. Measure in inches for UK sizing.
1.Measure Your Underbust (Band Size)
Wrap the tape measure firmly around your ribcage, directly underneath your breasts. Keep it level with the floor. Breathe out naturally and take a snug but comfortable reading.
If your measurement is an odd number, round up to the nearest even number. For example 33 inches becomes 34. That even number is your band size.
2.Measure Your Bust (Overbust)
Wrap the tape loosely around the fullest part of your breasts, usually across the nipple line. Keep the tape parallel to the floor and do not pull it tight. Let it sit gently against the skin.
3.Find Your Cup Size
Subtract your band measurement from your bust measurement. The difference gives you your cup size.
| Difference (inches) | UK Cup Size |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD |
| 6 | E |
| 7 | F |
| 8 | FF |
| 9 | G |
| 10 | GG |
| 11 | H |
So if your band is 34 inches and your bust is 38 inches, the difference is 4, making you a 34D.
How to Use This Calculator
Using our UK Bra Size Calculator is simple:
- Enter your underbust measurement (band size)
- Enter your bust measurement (overbust)
- Select your preferred unit, inches or centimetres
- Choose your sizing system, UK, US, EU or AU
- Hit Calculate Size for your instant result
The calculator also shows your sister sizes and adjusts for pregnancy and weight changes if you use the advanced options.
UK Bra Size Chart : Band and Cup Sizes Explained
UK bra sizes combine a number (band size) and a letter (cup size). The number refers to your underbust measurement in inches. The letter reflects the volume difference between your underbust and bust.
Common UK band sizes run from 28 to 46. Cup letters in the UK system go: AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K.
This matters because the UK system is one of the most comprehensive in the world for larger cup sizes, which is why many women with fuller busts prefer to shop from UK brands like Panache, Freya and Elomi even when buying internationally.
Understanding UK Cup Sizes, The DD System
This is where UK sizing confuses people who are used to US sizing. After D, the UK does not jump straight to E or go DD then DDD. Instead it follows a consistent pattern:
The UK cup system is used by many leading European brands including Panache, Freya and Fantasie, making it one of the most widely adopted systems for larger cup sizes.
A cup letter on its own means nothing without the band number. A 32D and a 38D share the same letter but the 38D has significantly more cup volume. Size and volume always go together.
What Does a Good Bra Fit Feel Like?
A well-fitting bra should feel comfortable from the moment you put it on. No pinching, no riding up, no digging in. Here is what to check:
The Band
provides around 80% of your support. It should sit straight and level across your back. You should be able to slide exactly two fingers underneath, no more, no less. If it rides up at the back, the band is too loose.
The Cups
should fully enclose your breast tissue with no spillage over the top or sides and no empty, wrinkled fabric inside. If your breast tissue is spilling out, go up a cup size. If there is excess space, go down one.
The Gore
is the central bridge connecting the two cups. It must lie flat against your sternum. If it lifts away from your chest, your cups are too small.
The Straps
should rest comfortably on your shoulders without digging in or slipping off. If they dig in, your band is likely too loose and the straps are overcompensating for the missing support.
Sister Sizing: The Fitting Trick Most Women Never Learn
Women's breasts change in size during the menstrual cycle, weight fluctuation and life stages, meaning a single fixed size rarely works perfectly forever. Sister sizing helps you fine-tune your fit when your calculated size is close but not quite right.
A sister size keeps the same cup volume but adjusts the band. When you go up a band size, you must go down a cup letter to keep the same volume. When you go down a band size, go up a cup letter.
Example:
- If 34D fits in the cup but the band feels too tight: try 36C
- If 34D fits in the cup but the band feels too loose: try 32E
All three sizes hold the same cup volume, only the band changes.
| Smaller Band | Same Cup Volume | Larger Band |
|---|---|---|
| 30E | 32D | 34C |
| 34FF | 36F | 38E |
| 36G | 38FF | 40F |
Sister sizing is also useful when your exact size is out of stock. It is one of the most practical bra fitting tools and one of the least talked about.
Why Your Bra Size Keeps Changing
Many women are surprised to find their size shifts over time. This is completely normal. Here are the main reasons:
- •Hormonal fluctuations during the menstrual cycle: cause breast tissue to swell and retain water. Breast volume can increase noticeably in the days leading up to your period, sometimes by a full cup size. Many women find it helpful to own bras in two slightly different sizes.
- •Weight changes: affect breast volume significantly because breasts contain a mix of glandular tissue and fat. Even a small weight change of 4 to 6 kg can alter both your cup size and band size.
- •Pregnancy and breastfeeding: cause major sizing changes throughout. Most women need to memorize multiple times during pregnancy and again after breastfeeding ends.
- •Age and elasticity: play a role too. Over time, breast tissue naturally loses density and firmness, which affects both shape and how a bra fits.
- •Brand inconsistency: is also very real. A 34D in one brand will not always match a 34D in another. UK lingerie brands in particular can vary considerably from high-street chains. Always measure rather than assuming your size transfers between brands.
UK vs US vs EU Bra Sizes : Key Differences
If you buy lingerie from international brands or shop online, understanding how sizing systems differ saves a lot of frustration.
When shopping abroad or from international websites, always check the brand's own size chart rather than relying on a general conversion.
Health Risks of Wearing the Wrong Bra Size
This section is one most bra fitting pages skip entirely, but it genuinely matters.
More than 80% of women wear the wrong bra size. More than 50% of women suffer from breast pain, usually due to poorly fitting bras giving insufficient support. And 20% of women suffer from frictional breast injuries caused by poor fitting or inappropriate bras.
Wearing a band that is too tight can restrict breathing and put pressure on the rib cage. A band that is too loose offers no real support, forcing the straps to carry all the weight, which leads to shoulder, neck and upper back pain.
Cups that are too small compress breast tissue against the chest wall. Over time this can cause skin irritation, discomfort during exercise and poor posture as the body adjusts to compensate.
A properly fitted bra also makes a measurable difference during physical activity. According to a University of Portsmouth study, unsupported breasts can move up to 14 centimetres during vigorous exercise, which can lead to permanent stretching of the skin and ligaments that support the breasts.
Getting your size right is not just about comfort, it is genuinely good for your body.
Bra Sizes for Special Circumstances
During Pregnancy and Breastfeeding
Breast size typically increases by one to two cup sizes during pregnancy and more so during breastfeeding. The band size may also increase. Standard sizing rules still apply, but you should measure at least once per trimester and again when breastfeeding begins and ends. Look for bras with wider bands and more cup coverage during this time.
After Mastectomy or Breast Surgery
Women who have undergone mastectomy, lumpectomy or breast reconstruction have specific fitting needs that a standard calculator may not fully address. Post-mastectomy bras are designed with features like pockets for breast forms and softer fabrics against sensitive skin. Many specialist UK lingerie fitters and brands offer dedicated fitting services for this. Organisations like Breast Cancer Now and Macmillan Cancer Support provide guidance on finding the right support.
Larger Cup Sizes (E Cup and Above)
Standard high-street bra ranges often stop at D or DD. If your calculated size is E cup or above, seek out specialist UK brands such as Panache, Freya, Elomi, Curvy Kate, and Fantasie. These brands are built around the UK cup sizing system and offer genuine structural support across a wide range of band and cup combinations.
Frequently Asked Questions
Related Calculators
References
- University of Portsmouth Research Group on Breast Health. Breast Biomechanics and the Importance of Sports Bra Support. port.ac.uk
- Triumph International. Bra Sizing and Fitting Guide UK. uk.triumph.com
- KnockerLocker. Sports Bra Fitting Guide and UK Bra Size Calculator. knockerlocker.co.uk
- Breast Cancer Now. Post-Mastectomy Bra and Breast Form Guidance. breastcancernow.org
- Macmillan Cancer Support. Breast Prostheses and Bras After Surgery. macmillan.org.uk
- British Lingerie Association. UK Bra Sizing Standards. britishlingerie.co.uk
- Gitnux Market Data. Bra Size Statistics 2026, Global and UK Data. gitnux.org