UK Bra Size Calculator
Enter your underbust and bust measurements below. Our AI calculator instantly gives you your UK bra size, sister sizes, and personalised fitting tips — in cm or inches.
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.
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.