1
Measure Your Under Bust
Measure snugly around your ribcage, right where your bra band sits. Keep the tape level and pull it firmly against your skin. Round to the nearest even number to find your correct UK band size.
Free · UK Standard Sizing · Instant Results
UK Bra Size Calculator
Find Your Perfect Fit
Two measurements and about thirty seconds is all it takes. Type your underbust and bust into the free UK bra size calculator— centimetres or inches, whichever you measured in — and you'll instantly see your UK band, cup letter, sister sizes, and the EU equivalent. No tape measure experience required.
Free foreverAccurate UK Sizing StandardsUK + EU sizes
UK Bra Calculator
Enter your underbust and bust measurements below. The calculator works out your UK band and cup, flags your nearest sister sizes, and gives you the EU equivalent — all in one go.
Enter Your Measurements
Measure snugly around your ribcage, directly under your bust.
Measure around the fullest part of your bust, keeping the tape level.
You'll get your UK size, international equivalents, sister sizes, and fitting tips.
🔒 Your measurements are never saved or shared — calculations happen entirely in your browser.
How to Measure Your Bra Size
All you need is a soft tape measure — a piece of string and a ruler works too. Two measurements, done in under a minute.
2
Measure Your Full Bust
Wrap the tape around the fullest part of your bust. Keep it gentle but stable so it doesn't compress your tissue. The gap in inches between this and your underbust determines your cup size.
Comprehensive Reference
Looking for the Full UK Bra Size Chart?
We maintain the complete 28AA to 46K reference matrix, including specialist store availability, sister size conversions, and brand-specific fit notes for M&S, Bravissimo, Freya, and Panache.
How to Calculate Your UK Bra Size
Calculating your size is a simple two-step process: find your band by measuring your ribcage, then find your cup by measuring the fullness of your bust. Our tool does the heavy lifting for both inches and centimetres, automatically mapping your measurements to the correct UK band and cup, while also showing you sister sizes and the corresponding EU equivalents.
To determine your band, round your underbust measurement to the closest even number (e.g., 31” becomes 32”). Your cupis determined by the inch difference between your full bust and your underbust: 1” equals an A, 2” a B, and so on. Note that UK cups follow a unique sequence—AA, A, B, C, D, DD, E, F—which differs from US or EU conventions.
We bypass outdated formulas, such as adding extra inches to your ribcage measurement, which often leads to poor support and sliding bands. By working strictly from your natural measurements, we ensure a fit that anchors correctly against your body. For a deeper look, check our measurement guide or view our comprehensive size reference.
Why the “+4” Rule is Outdated
Many older sizing guides suggest adding four inches to your underbust to find your band. This practice originated in the early 20th century, when bras were crafted from rigid, inelastic fabrics that provided no give. Manufacturers added extra room so the bra was wearable, but this is entirely unnecessary with today's flexible elastane and Lycra blends.
Applying the +4 rule today typically results in a band that is significantly too loose. A loose band fails to sit flat against your ribcage, causing it to slide up your back and placing excessive strain on the shoulder straps, which leads to discomfort, sagging, and frequent readjustments.
Modern professional fitting centers, such as those at leading UK lingerie boutiques, calculate size based on your actual ribcage measurement. Our calculator follows this modern standard, which is why your result might feel firmer or different than what you have worn previously. A proper, firm band ensures the underwire sits accurately in your crease and provides the support your body needs.
The 5-Point Bra Fit Checklist
A well-fitting bra should be secure and comfortable without constant adjustment. Use this checklist to verify your fit.
1. The Underband
Your band should sit perfectly level across your back. If it arches upward toward your shoulders, the band is too large. You should be able to fit two fingers snugly between the band and your skin.
2. The Underwires
The wires should sit flat against your ribcage, framing your breast tissue entirely. If the wire rests on soft tissue rather than bone, or feels like it is pinching, you likely need a larger cup size.
3. The Cups
Your breast tissue should be fully enclosed without spilling over the top or sides. Any puckering or fabric gaps at the top indicate that the cup size is too large for your shape.
4. The Centre Gore
The centre piece connecting the cups should sit flush against your sternum. If it floats away from your body, your cup size is almost certainly too small to accommodate your breast tissue.
5. The Straps
Straps should be secure but not painful. They are designed to support about 20% of the weight; if they are digging into your skin, the band is likely too loose and failing to provide the main support.
All Tools & Guides
Fit Problems
Diagnose & fix fit issues
Size Converter
UK to US, EU, AU, FR
Sister Sizes
Same volume, different band
Maternity Bra
Pregnancy & nursing sizes
Size Guide UK
Full 28AA to 46K chart
Measuring Guide
Step-by-step at home
Sports Bra Guide
Low, medium & high impact
Cup Visualiser
See AA to K side by side
First Bra Guide
Teen & junior fitting
Brand Guide
M&S, Bravissimo, Next…
FAQ
Bra Size FAQ
The most common questions about UK bra sizing — answered simply.
You need two measurements and a soft tape. First, wrap the tape snugly around your ribcage, directly under your bust — that's your underbust. Then measure around the fullest point of your bust, keeping the tape level. Type both numbers into the UK bra size calculator above (cm or inches both work) and you'll get your UK band size, cup letter, sister sizes, and EU equivalent instantly.