Bra Size Calculator Guide - UK US EU Conversion

Studies suggest up to 80% of women wear the wrong bra size. Getting properly fitted can improve comfort, posture, and how clothes fit.

How to Measure

Band Size

1. Measure around your ribcage, directly under your bust
2. The tape should be snug but comfortable
3. Round to nearest whole number
4. If odd, round up to even number for UK sizing

Cup Size

1. Measure around the fullest part of your bust
2. Keep tape level and don't pull tight
3. Subtract band from bust measurement
4. Each inch difference = one cup size

Cup Size Chart (UK)

Band Size Conversion

Signs of Wrong Size

• Band riding up: Band too loose, try smaller
• Straps digging in: Band too loose (band should support, not straps)
• Cup spillage: Cup too small, try larger cup
• Gaps in cup: Cup too large, try smaller cup
• Underwire digging: Wrong cup size or shape

How Bra Size Calculations Work: The Methodology

Bra sizing uses a two-component system: the band size (a number) and the cup size (a letter). The band size represents the circumference of your ribcage directly below your bust, while the cup size represents the difference between your bust measurement and your band measurement. Together, they describe both the frame you need to fit around your torso and the volume needed to accommodate your bust.

In the UK sizing system, band sizes run in even numbers from 28 to 48 (inches). To determine your band size, measure around your ribcage, directly under your bust, with the tape snug but not tight. If the measurement is an even number, that is your band size. If it is odd, round up to the next even number. Some fitting methods add 4-5 inches to the underbust measurement, but this older technique is now considered outdated by most professional fitters, as it tends to result in a band that is too loose.

Cup size is determined by measuring around the fullest part of the bust (typically at nipple level) while wearing an unpadded bra or no bra, keeping the tape level. Subtract the band measurement from this bust measurement. Each inch of difference corresponds to one cup size increment: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD, 6 inches = E, 7 inches = F, 8 inches = FF, 9 inches = G, and so on. The UK system uses double letters (DD, FF, GG, HH, JJ, KK) to extend the range, unlike the US system which uses consecutive single letters.

The concept of "sister sizes" is important for understanding how bra sizing works volumetrically. Sister sizes share the same cup volume but have different band sizes. For example, 34D, 36C, and 32DD all have the same cup volume. If your usual band size is not available, you can go up a band size and down a cup size (or vice versa) to find a sister size that provides a similar fit. However, the band support will differ, so sister sizing is a compromise rather than an ideal solution.

It is worth noting that bra sizing is not an exact science. Different manufacturers use different patterns, materials, and size specifications. A 34D from one brand may fit differently from a 34D from another. This is why professional fitting is recommended over relying solely on measurements, and why you should always try on bras before purchasing.

UK-Specific Context: Bra Fitting in Britain

The UK has one of the most extensive bra size ranges in the world, with specialist retailers like Bravissimo stocking sizes from 28D to 40L. This reflects both the physical diversity of the UK population and a strong fitting culture that has developed over decades. The UK bra market is worth approximately £2.4 billion annually, with the average British woman spending £4,000-£5,000 on bras over her lifetime.

Professional bra fitting is widely available and free at most UK high street retailers. Marks and Spencer, which sells approximately one-third of all bras purchased in the UK, offers free in-store fittings. Bravissimo specialises in D-cup and above with expert fitters. John Lewis, Debenhams, and independent lingerie boutiques also offer fitting services. Many UK women find that a professional fitting changes their bra size significantly -- Bravissimo reports that the majority of women they fit move to a different size from what they were wearing.

The most common bra size in the UK is 36DD, a significant increase from the 34B average reported in the early 2000s. This shift reflects several factors: better fitting awareness (many women previously wore too-large bands and too-small cups), population weight increases, and changes in bra construction and marketing that have made larger cup sizes more accessible and destigmatised.

UK consumer rights protect bra purchases. Under the Consumer Rights Act 2015, bras purchased online can be returned within 14 days for a full refund (under the Distance Selling Regulations). In-store returns depend on the retailer's policy, but most UK bra retailers offer generous exchange policies. When shopping online, buying two or three sizes to try at home and returning the non-fitting ones is a common and accepted practice.

Bra recycling is a growing movement in the UK. Organisations such as Against Breast Cancer and Smalls for All collect used bras for recycling and redistribution. Many M&S stores have bra recycling bins. Given that the average bra has a useful life of approximately 6-12 months with regular wear, and UK women own an average of 6-8 bras, a significant volume of bras enters the waste stream each year.

Worked Examples: Finding Your UK Bra Size

Common Mistakes and Tips

Frequently Asked Questions

Why do UK and US cup sizes differ?

UK and US sizing systems diverge after D cup. The UK system uses double letters (DD, E, F, FF, G, GG, H, HH, J, JJ, K, KK), while the US system generally uses consecutive single letters (DD/E, DDD/F, G, H, I, J, K, L, M). A UK 34F is equivalent to a US 34G, and a UK 34GG is equivalent to a US 34J. EU sizing uses centimetre-based band sizes (e.g., UK 34 = EU 75) and a different cup letter sequence. Always check which sizing system a brand uses before ordering, especially when buying from international retailers online.

What is the best bra for large busts in the UK?

For cup sizes DD and above, look for bras with reinforced side panels, wider straps, multiple hook-and-eye closures (3-4 hooks), and firm underwire. UK specialists include Bravissimo (up to L cup), Elomi (up to KK cup), Panache (up to K cup), and Curvy Kate (up to KK cup). M&S stocks a good range to G cup at affordable prices. A well-fitted bra in the correct size from a specialist brand will provide significantly better support and comfort than a poorly fitting bra from a generic retailer.

How many bras should I own?

Most fitting experts recommend owning at least 3-4 everyday bras and rotating them daily. Wearing the same bra two days in a row does not allow the elastic to recover, shortening the garment's lifespan. Additionally, most women benefit from owning at least one sports bra, one strapless or multiway bra, and one special occasion bra. Budget approximately £100-200 per year for bra replacement if wearing them daily.

Should I wear a bra during sleep?

There is no medical evidence that wearing a bra to bed is either beneficial or harmful. It does not prevent sagging (which is caused by genetics, age, and gravity, not bra use) and it does not cause breast cancer (this is a persistent myth with no scientific basis). If you find a soft, non-wired sleep bra comfortable, there is no reason not to wear one. If you prefer sleeping without a bra, that is equally fine. The choice is entirely personal.

Where to Get Fitted UK

UK Bra Prices 2025

Caring for Your Bras

• Hand wash: Or use a lingerie bag on delicate cycle
• Never tumble dry: Heat damages elastic and underwire
• Rotate bras: Own 3-4 and don't wear same one two days running
• Replace annually: Bras lose support after 6-12 months of regular wear
• Store flat: Don't fold cups into each other

Dr. Sarah Chen, PhD

Research Scientist, Public Health

Sarah holds a PhD in Public Health from the University of Edinburgh and has published research on UK health metrics and obesity trends. She translates complex medical data into practical, accessible guidance for everyday readers.