Two measurements give you a starting size in UK lettering. Our guides then help you check the band, cups and wires, so you end up in a bra that fits and not just a number.
Enter your underbust and bust in inches or centimetres. We use the number on the tape as it is, with nothing added.
Snug around your ribcage, directly under your breasts, tape level all the way round.
Around the fullest part, tape resting on the skin without squashing. Braless or in an unpadded bra.
Treat it as the first size to try on, not a verdict. Brands cut differently and breast shape changes how a cup sits. Put the bra on, scoop and swoop, then run the five-point fit check.
Want the method, worked examples and common mistakes alongside the tool? Use the full bra size calculator page.
Each tool answers one question, and each tells you what to check next.
Two measurements in inches or cm give your UK starting size, sister sizes and international equivalents.
Size Chart UK Bra Size ChartEvery UK band and cup in one printable chart, with a lookup that finds your size from your measurements.
Sister Sizes Sister Size Chart & CalculatorPick your size and see which neighbouring sizes hold the same cup volume on a tighter or looser band.
Conversion International Bra Size ChartConvert any UK size to US, EU, French and Australian labelling, with the full comparison tables.
Sports Bras Sports Bra Size CalculatorTurns your everyday size into a sports bra recommendation by impact level and bra construction.
Maternity & Nursing Nursing Bra Size CalculatorStage-aware sizing for pregnancy and breastfeeding, with the room to allow and when to re-measure.
Calculator Bra Size Calculator in cmA centimetre-first calculator and chart, with UK and European sizes side by side.
Three things we do differently from most size guides.
Many size guides still add four or five inches to the underbust. A University of Portsmouth study found that approach overestimated band size in 76% of the women tested and underestimated cup size in 84%. We use your real measurement. Read why.
A tape measure cannot see breast shape, and no two brands cut alike. Every result here is labelled a starting size and comes with the checks that confirm it. How accurate calculators really are.
UK cups run D, DD, E, F, FF, G. US and European labels do not. Everything here is in UK lettering, with conversions when you shop abroad. See the conversion chart.
The guides most people need first. Browse all guides, fit help, cup sizes or brand guides.
The full step-by-step method: underbust, bust, rounding rules, worked examples and the mistakes to avoid.
Fit How Should a Bra Fit?The five-point fit check — band, cups, gore, wires and straps — and what a good fit actually feels like.
Diagnose Signs Your Bra Doesn't FitA symptom-by-symptom checklist. Find what you are seeing and jump to the fix.
Sister Sizes What Are Sister Sizes?Why 32D, 34C and 36B hold the same volume, and the one-step rule for using a sister size well.
Reference UK Cup Sizes in OrderAA to KK in the correct UK order, with the inch difference behind each letter.
Conversion UK vs US Bra SizesIdentical up to a D cup, different after it. How to read a label and avoid ordering the wrong cup.
Your real underbust measurement, rounded to the nearest even number, is your band. The difference between your bust and that band gives your cup, at one cup per inch. Nothing is added to the underbust. The older habit of adding four or five inches was shown in a University of Portsmouth study to overestimate the band for most women.
Usually because of the method. Some fitters and size guides still add inches to the underbust, which gives a looser band and a smaller cup letter. Brands also cut differently, so the same size can fit differently from one label to the next. Use your result as the first size to try on, then check the fit.
No to both. We do not sell bras, and the calculators run entirely in your browser, so the numbers you type are never sent to us.
No calculator can promise that. Two measurements cannot capture breast shape, and brands vary. What a good calculator gives you is the right place to start, which is why every result here links to a fit check.