BraSizeConversion

Bra Size Calculator

7 sizing systems25+ country calculatorsBands 28-60, cups AA-PZero data stored

Enter your snug underbust and your bust at its fullest point, and this calculator returns your starting size in all 7 international systems at once, with sister sizes included. It uses the modern no-add method: your band is your actual underbust measurement, not your measurement plus four inches.

Results update live as you type, and nothing you enter leaves your browser. Measure braless or in a non-padded bra, tape snug and level; the measuring guide below shows exactly where the tape sits.

Enter your measurements

This calculation runs entirely in your browser. Your measurements are never stored or sent anywhere.

How we calculate: the exact method

Band: your underbust measurement, rounded to the nearest even number for US and UK sizing, and to the nearest 5 centimeters for EU, JP and KR. French bands add 15 to the EU number, and Australian bands use dress-number logic where an AU 10 equals a US 32. We do not add four or five inches to the underbust. That plus-four habit dates from an era of non-stretch fabrics, and on modern elastic bands it produces bands too loose to support anything.

Cup: the difference between your bust and band measurements, where each inch of difference is one cup letter. One inch is an A, two a B, three a C, four a D. After D the ladders diverge by system: US runs DD, DDD, G while UK runs DD, E, F, FF, G, and Japanese and Korean letters run about one letter fuller than European for the same difference. That divergence is exactly why this calculator shows all 7 systems side by side.

What to do with your result

Treat the number as a fitting-room starting point, not a verdict. A correctly sized band should feel firmly snug on the loosest hook when new, the center gore should sit flat against your sternum, and all tissue should sit inside the wire line. If any of those fail, the fit problem solver diagnoses which direction to adjust.

Then account for brands: a 34DD at Victoria's Secret is cut to a different depth than a 34DD at Freya, even though the label matches. The brand size decoder translates your measured size into a starting size for ten major brands.

Frequently asked questions

How do I calculate my bra size?
Measure your underbust snugly, then your bust at the fullest point. Your band is the underbust rounded to sizing convention, and each inch of difference between bust and band is one cup letter: 1 inch A, 2 B, 3 C, 4 D.
Should I add 4 inches to my underbust measurement?
No. The plus-four method was designed for rigid vintage fabrics. Modern bands are elastic and support from firmness, so your band size is your actual underbust measurement rounded to the nearest even number.
Why does the calculator show 7 different sizes?
Because US, UK, EU, French, Australian, Japanese and Korean systems label the same body differently. The bands use different numbering and the cup letters diverge after D, so one converted label per system is the only accurate answer.
Is this bra size calculator really private?
Yes. The math runs in your browser using JavaScript on your device. Your measurements are never transmitted, stored or logged anywhere, and there is no account or email to give.
Next steps

Last updated August 2026.