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Bra Size Calculator

Turn two tape-measure readings into an estimated bra size, see what it's called in other countries' sizing, and find the sister sizes to try if the fit isn't quite right.

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How to use the bra size calculator

  1. Choose inches or centimeters for your measurements.
  2. Measure your underbust: wrap the tape snugly around your ribcage, right under your bust, keeping it level all the way round. Breathe out normally.
  3. Measure your bust: wrap the tape loosely around the fullest part, without squashing anything. Measuring while wearing an unpadded bra helps.
  4. Pick the band method. The modern method is what most specialist fitters use today; the traditional "+4" method is still printed on some older size charts.
  5. Read your estimated size, the equivalents in other sizing systems, and your sister sizes.

How bra size is calculated

Band = underbust rounded to the nearest inch, then up to an even number (traditional method: + 4 in if even, + 5 in if odd) Cup = bust − band, rounded to the nearest inch 0 = AA, 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = E (UK) … EU band = 70 for a UK/US 32, and 5 more for each 2 in FR band = EU band + 15 AU band = UK band − 22

Each inch of difference between the bust and the band is one cup size. Bands come in even numbers, so an odd underbust is rounded up. The US and UK use the same band numbers but start to name cups differently after D: the UK goes DD, E, F, FF, G, while most US brands go DD (or E), DDD (or F), G, H. EU, French and Australian sizes follow the UK cup sequence in their own lettering, so the calculator converts using the common brand charts.

Worked example

The defaults are an underbust of 32 in and a bust of 36 in, with the modern method:

  • Band: 32 rounds to 32, which is already even, so the band is 32
  • Cup: 36 − 32 = 4 in, which is a D
  • US and UK size: 32D
  • EU: 70D, French: 85D, Australian: 10D

In centimeters, 81 cm and 92 cm are 31.9 in and 36.2 in, which give the same band of 32 and a difference of 4.2, rounded to 4, so the EU size is 70D. With a 38 in bust instead, the difference is 6 in: 32DDD/F in US sizing and 32E in UK sizing.

The traditional method adds 4 in to an even underbust, so 32 becomes a 36 band, and 36 − 36 = 0 gives 36AA. That shows why the method fell out of favor: it tends to give a band that's too loose and cups that are too small.

Size conversion chart

Bust − band US UK and AU EU and FR
1 in A A A
2 in B B B
3 in C C C
4 in D D D
5 in DD/E DD E
6 in DDD/F E F
7 in G F G
8 in H FF H
9 in I G I
10 in J GG J
US/UK band 28 30 32 34 36 38 40
EU 60 65 70 75 80 85 90
FR 75 80 85 90 95 100 105
AU 6 8 10 12 14 16 18

Sister sizes

A sister size has the same cup volume on a different band. Going one band size up and one cup letter down keeps the volume the same: 32D, 34C and 30DD (UK) all hold about the same. If the cups of your size fit but the band rides up your back, try the sister size with a smaller band and a bigger cup letter. If the band digs in, go one band up and one cup down.

Frequently asked questions

How should a bra fit?

The band should sit level around your body and feel snug on the loosest hook, so you can tighten it as it stretches. The cups should hold all of the breast tissue without gaps or spilling over, and the center panel should lie flat against your breastbone. Most of the support comes from the band, not the straps.

Why is my size different between brands?

There's no single sizing standard. Brands use different band stretch, cup shapes and labeling, and US brands in particular differ in how they name cups above D. Treat the result as a starting point and try a size either side, or use the brand's own chart.

Should I measure in inches or centimeters?

Use whichever your tape shows; the calculator converts centimeters to inches before working out the size. If you shop mostly in Europe, the EU size is the one to look for on labels.

How often should I measure myself?

Every six months to a year, and after weight changes, pregnancy, breastfeeding or starting a new exercise routine. Bands stretch with wear, so a bra that fit when new may need replacing after about a year of regular use.

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