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Bra size calculator

Two measurements, your underbust and your bust, give your bra size in seven systems, and the sister sizes that hold the same cup volume.

EU
75B
FR
90B
IT
3B
UK
34B
US
34B
AU
12B
JP
B75

Sister sizes (same cup volume): 70C and 80A in EU sizing. Band rounded to 5 cm, cup from the difference (EN 13402-3).

How the size is computed

The band is your underbust rounded to the nearest 5 cm (EN 13402-3). The cup comes from the difference between bust and underbust: AA for 10 to 12 cm, then one letter for every 2 cm more.

Other systems follow from the EU size: French bands are 15 more, Italian bands count from 0, UK and US bands are in inches, Australian bands are the UK band minus 22. Cup letters split differently after D: UK goes DD, E, F, FF; US goes DD, DDD, G.

Sister sizes keep the same cup volume: one band down and one cup up, or one band up and one cup down. This is the calculation Find my size runs in Ruban Size on bra charts.

Bra size conversion chart

Equivalents from the EU size (EN 13402-3). Brands vary; a brand’s own chart wins.
EUUKUSFranceItalyAustraliaJapan
65A30A30A80A1A8AA65
65B30B30B80B1B8BB65
65C30C30C80C1C8CC65
65D30D30D80D1D8DD65
65E30DD30DD80E1E8DDE65
65F30E30DDD80F1F8EF65
65G30F30G80G1G8FG65
70A32A32A85A2A10AA70
70B32B32B85B2B10BB70
70C32C32C85C2C10CC70
70D32D32D85D2D10DD70
70E32DD32DD85E2E10DDE70
70F32E32DDD85F2F10EF70
70G32F32G85G2G10FG70
75A34A34A90A3A12AA75
75B34B34B90B3B12BB75
75C34C34C90C3C12CC75
75D34D34D90D3D12DD75
75E34DD34DD90E3E12DDE75
75F34E34DDD90F3F12EF75
75G34F34G90G3G12FG75
80A36A36A95A4A14AA80
80B36B36B95B4B14BB80
80C36C36C95C4C14CC80
80D36D36D95D4D14DD80
80E36DD36DD95E4E14DDE80
80F36E36DDD95F4F14EF80
80G36F36G95G4G14FG80
85A38A38A100A5A16AA85
85B38B38B100B5B16BB85
85C38C38C100C5C16CC85
85D38D38D100D5D16DD85
85E38DD38DD100E5E16DDE85
85F38E38DDD100F5F16EF85
85G38F38G100G5G16FG85
90A40A40A105A6A18AA90
90B40B40B105B6B18BB90
90C40C40C105C6C18CC90
90D40D40D105D6D18DD90
90E40DD40DD105E6E18DDE90
90F40E40DDD105F6F18EF90
90G40F40G105G6G18FG90
95A42A42A110A7A20AA95
95B42B42B110B7B20BB95
95C42C42C110C7C20CC95
95D42D42D110D7D20DD95
95E42DD42DD110E7E20DDE95
95F42E42DDD110F7F20EF95
95G42F42G110G7G20FG95

Equivalents from the EU size (EN 13402-3). Brands vary; a brand’s own chart wins.

How to measure

  1. Underbust

    Tape snug and level right under the bust, breathing out.

  2. Bust

    Tape level across the fullest point, not pulled tight, wearing a bra without padding.

  3. Read both in cm

    Or in inches: the calculator switches units for you.

Questions

Why do UK and US cups differ after D?

Both start AA, A, B, C, D. Then UK sizes go DD, E, F, FF, G while US sizes go DD, DDD, G. The same cup can carry two letters.

What are sister sizes?

Sizes with the same cup volume on a different band: 75C has 70D and 80B as sisters. Useful when a band feels too tight or too loose.

Should the band feel tight?

Snug: the band carries most of the support. If it rides up at the back, it is too loose; try the sister size with a smaller band.

Does this work for sports or maternity bras?

Sports bras are often sized S, M, L from the same two measurements, as in the sports bra template of Ruban Size. Maternity and nursing bras: measure again as your size changes.

Read more

Put it on your product pages.

Ruban Size does these conversions inside your size guide, in Find my size, in 22 languages. Free for 5 size charts.

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