UK Bra Size Calculator
Our UK bra size calculator uses modern professional fitting standards to instantly find your correct band and cup size. Enter your underbust and overbust measurements in inches or cm below to calculate your UK bra size, EU equivalent, sister sizes, and custom fit suggestions.
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 Use the Calculator
Follow these 3 simple steps — takes under 2 minutes.
Measure Underbust
Wrap a soft tape under your bust, directly on your ribcage. Record in cm or inches.
Measure Bust
Measure around the fullest part of your bust. Keep the tape snug but comfortable.
Get Your Size
Enter both numbers above. The calculator instantly shows your UK size, sister sizes and tips.
Pro Fitting Tips
Always measure on bare skin or a non-padded bra for accuracy.
Remeasure every 6 months — your size changes with weight and age.
The band provides 80% of support. A too-loose band means too-tight straps.
The centre gore (front middle) should lie flat against your sternum.
You should be able to fit two fingers under the band — no more.
Start on the loosest hook so you can tighten the band as it stretches.
Frequently Asked Questions
What is a bra fitting calculator?+
A bra fitting calculator is an online tool that uses your underbust and overbust measurements to determine your correct band and cup size. It replaces old retail formulas that often add artificial inches to the band size.
How do I measure my bra size in inches?+
To measure in inches, wrap a soft measuring tape snugly around your ribcage directly under your bust for your band size. Then, measure around the fullest part of your bust for your cup size. Subtract the band size from the bust size to find your cup size letter (e.g. 1" difference = A, 2" = B, 3" = C, 4" = D, 5" = DD).
How do I use a bra size calculator in cm?+
Using a bra size calculator in cm is exactly the same as in inches. Enter your underbust and bust measurements in centimetres. Our calculator automatically converts the values into standard UK band sizes (in inches) and cup letters.
What is the most accurate bra sizes calculator?+
The most accurate bra size calculator uses your direct ribcage (underbust) measurement to establish the band size, and compares it directly to the fullest overbust measurement for the cup size. This modern fitting method is trusted by lingerie fitters across the UK.
Expert Reviewed Fitting
This calculator is vetted by industry fitters to ensure maximum size calculation accuracy.
Eleanor Vance
Certified Bra Fitter & Lingerie Consultant
Over 12 years of professional fitting experience at leading UK lingerie retailers, including Bravissimo and Marks & Spencer. Specially certified in maternity, teen first-fit, and post-surgery supportive consultations.
Sizing Math & Rounding Logic
Our calculator implements the industry-standard **modern fitting method** rather than the obsolete "plus-4" retail formula. Band sizes are derived directly from snug ribcage measurements in inches (rounded to the nearest even number). Cup sizes are calculated using the precise 1-inch difference increments between fuller bust and underbust measurements (e.g. 4" = D, 5" = DD, 6" = E).
Sourced Claims & Studies
Medical and biomechanical research shows that up to **80% of UK women wear the wrong bra size**. According to breast health clinical research from the **University of Portsmouth (Department of Sport and Exercise Science)**, properly fitted encapsulation support reduces vertical breast movement by up to 59%, significantly preventing exercise-induced breast discomfort and cooper's ligament stretching.