Bra Size Calculator

You only need a soft measuring tape, a mirror and five quiet minutes. Wear an unpadded bra that fits reasonably well, or no bra at all, and take both measurements while standing relaxed.

1. Band (underbust): Run the tape around your ribcage, directly under your breasts, where the band of your bra sits. Keep it level all the way around and snug, not tight. Breathe out and read the number in centimetres.
2. Bust (overbust): Wrap the tape around the fullest part of your bust, usually across the nipples. Stay relaxed and do not pull tight, or you will flatten the tissue and end up with a cup that is too small.

Your band size comes from the underbust number. Your cup comes from the difference between bust and underbust. That difference is the only thing that decides the cup letter, not the bust measurement on its own.

This is the heart of it. First the band, then the cup. The band measurement in centimetres maps to the international labels like this.

The cup comes from bust minus underbust. The same difference can carry a different letter depending on the country, so check the right column.

Say your underbust is 74 cm and your bust is 92 cm. The band of 74 cm sits in the 73 to 77 row, so you are an EU 75, a UK and US 34, an FR 90.

The difference is 92 minus 74, which is 18 cm. Eighteen centimetres lands in the D row across all three systems, so your size reads EU 75D, UK 34D, US 34D, FR 90D. Same body, four labels.

Below D the letters mostly agree. From the fourth cup upward they drift apart, and this is where most online orders go wrong.

In the EU and German system the cups simply continue A, B, C, D, E, F, G. In the UK and US system, the cup after D is written DD, then the next ones become E, F and so on. So an EU E is usually a UK and US DD, and an EU F is roughly a UK E. If you only convert the band and assume the letter stays the same, you can end up one full cup off.

A few things trip almost everyone up.

• Band too loose. The band, not the straps, carries most of the support. If it rides up at the back, it is too big. Measure snug and trust the smaller band.
• Pulling the tape tight on the bust. This shrinks the difference and gives you a cup that is too small. Keep it relaxed.
• Ignoring the cup shift. See the section above. Always read the cup column for the country you are buying in.

Sister sizes are your friend when a bra fits in the cup but not the band. If you go down one band, go up one cup, and the other way around. A 75C, an 80B and a 70D all hold a similar cup volume, just on a different band. That gives you a backup size when your exact label is sold out.

Measurements give you a starting point, never a verdict. Brands cut differently, and a French label often runs tighter than a German one. Buy your calculated size, then check the fit in the mirror. The band should sit level and firm, the centre panel should lie flat against your breastbone, and nothing should spill over the top or gape at the edge. When in doubt, try your size plus the two sister sizes around it and keep the one that disappears under your clothes.