Advanced Bra Size Calculator UK | Find Your Perfect Fit Instantly

Most people in the UK wear the wrong bra size.
This calculator uses modern fitting logic, breast shape analysis, and UK sizing standards to give you a reliable starting size — plus sister sizes if the fit isn’t perfect.

Bra Size Calculator UK

Enter your measurements below to calculate your UK bra size. This calculator provides a starting size, along with sister sizes and international conversions.

1 Enter Your Measurements

Need help? Click here for measurement instructions.

1. Band Measurement (Underbust)

While wearing a non-padded bra, wrap a soft measuring tape snugly around your ribcage, directly under your bust. Make sure the tape is parallel to the floor. Breathe out fully.

2. Bust Measurement (Fullest Part)

Wrap the measuring tape around the fullest part of your bust (usually over the nipples). The tape should be comfortably loose, not digging in, and level all the way around.

Check our guide on How to measure your bra size

Choose Your Unit:
inches
inches

2 Select Your Breast Shape

Round
East West
Side Set
Slender
Bell
Asymmetric

Your Recommended UK Starting Size

Recommended Bra Styles for Your Shape

Your Sister Sizes 👯‍♀️

If the fit isn't perfect, one of these might be a better match.

Find more sister size options

International Size Conversions 🌍

Shopping abroad or online? Use this guide.

RegionBandCupFull Size
Click to show/hide conversions
Why Trust US?

More Than Just a Simple Bra Size Calculator

Expert-Designed

Our algorithm is based on professional fitting methods to give you a reliable starting point for shopping at all your favourite UK brands, including Marks & Spencer, Bravissimo, Boux Avenue, and John Lewis.

Personalised for Your Shape

We know that size is only half the story. Our calculator is one of the few to incorporate breast shape analysis, giving you recommendations that actually work for your body.

100% Private & Secure

Your comfort and privacy are our top priorities. Your measurements are never saved, stored, or shared. The entire calculation happens securely in your browser. Period.

Our Mission

Finding a bra that fits shouldn’t feel like an impossible task. We started this site after our own frustrating experiences in fitting rooms across the UK—from London to Manchester. Our mission is to empower you with free, accurate, and easy-to-understand tools and advice, so you can finally find the comfort and confidence you deserve.

From Our Bra Guides

Once you know your size, these guides help you understand fit, fix common issues, and choose bras that work best for your body.

Frequently Asked Questions

Our calculator is designed to be a highly accurate starting point for your bra fitting journey. It uses modern fitting logic that goes beyond simple measurements by incorporating breast shape analysis. However, because every bra brand fits slightly differently, we always recommend you use this result to try on bras and also test your sister sizes to find your absolute perfect fit.

This is the most common reaction we see! Research shows that a very high percentage of women are wearing the wrong bra size—most often, with a band that is too loose and a cup that is too small. It can be a shock to go from a 36C to a 32E, for example, but this often represents a much more supportive and comfortable fit. Trust the measurements and our common fit problems guide to learn what a correct fit should feel like.

For the most accurate results, you should measure while wearing a thin, non-padded bra. A molded T-shirt bra is perfect. Measuring without a bra can cause your bust to sit lower than it naturally would, which can skew the measurement. A heavily padded bra will add extra inches and give you an inaccurate result.

The most important next step is to try on bras in your new recommended size. Forget about the size you thought you were. When you try on the new bra, pay close attention to our fit checklist: the band should be snug and parallel to the floor, your breasts should completely fill the cups with no gaping or spilling, and the center gore should lie flat against your chest.

No, they don’t. Just like with clothes, there can be slight variations in sizing between brands. A 34D from Marks & Spencer might feel slightly different from a 34D at Bravissimo. That’s why we call our result a “starting point.” Once you find your size with one brand, you’ll learn if you need to adjust slightly for others.