Clothing / Fit
Bra Size Calculator: Underbust, Bust and Cup Systems
Enter underbust and bust measurements in centimetres or inches. Compare EN-style EU sizing with modern UK/US estimates and published French, Australian and Japanese schemes.
Bra Size Calculator: Underbust, Bust and Cup Systems: EU uses the nearest 5 cm band and 2 cm cup intervals based on the measured bust minus underbust. UK and US use the modern no +4 convention: nearest even inch band and 1 inch cup steps, showing adjacent cups between steps. FR/BE uses EU +15 for the band. AU/NZ uses UK band minus 22 and the single-letter sequence after F. JP uses 5 cm bands and 2.5 cm cup steps. Each system is calculated independently; these are not direct equivalents. Runs 100% locally in your browser with zero server file uploads.
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Measure comfortably snug just below the breasts, then around the fullest part of the bust without compressing it. This two-measurement estimate is a starting point.
Bust − underbust: 15.00 cm / 5.91 in
| System | Starting size | Method |
|---|---|---|
| EU | 80B | EN 13402-3:2004 style; nearest 5 cm band, 2 cm cups |
| UK | 32DD or 32E | Modern no +4; nearest even inch band, 1 inch cups |
| US | 32DD/E or 32DDD/F | Modern no +4; common cup-letter convention |
| FR / BE | 95B | Common convention: EU band + 15; EU cups |
| AU / NZ | 10DD or 10E | Common convention: UK band − 22; single letters after F |
| JP | C80 | JIS L 4006:1998 style; nearest 5 cm band, 2.5 cm cups |
EU / FR / BE: AA 10–12, A 12–14, B 14–16, C 16–18, D 18–20, E 20–22, F 22–24, G 24–26, H 26–28 cm. Shared boundaries use the larger cup; 28 cm is included in H. Bands shown: EU 60–125.
UK: AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K, KK, L, LL. US: AA, A, B, C, D, DD/E, DDD/F, G, H, I, J, K, L, M, N, O. AA is below 1 inch; A is 1 inch, B is 2 inches, and so on. Between whole-inch differences, both adjacent cups are shown. Bands shown: 28–50.
AU / NZ: AA, A, B, C, D, DD, E, F, G, H, I, J, K, using 1 inch steps. Some labels retain the UK double letters after F instead. JP: AA, A, B, C, D, E, F, G, H, I, centred on 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5 and 30 cm. JP uses the nearest centre, with ties upwards; bands shown: 60–120.
The modern UK/US method adds no inches to underbust. The traditional +4 method adds 4 inches to an even rounded underbust or 5 to an odd one, then compares bust with that band. It can produce a different band and cup. These results use each system independently, not a direct conversion of the EU result.
Band ties round upwards. The UK/US/AU estimate uses your bust minus underbust; it does not reproduce A Bra That Fits’ full six-measurement fitting method. US and AU cup letters are common conventions, not universal standards.
Fit varies by brand and style; get measured if unsure.
Sources checked 4 October 2026: EN 13402-3:2004, JIS L 4006:1998, and A Bra That Fits’ published sizing guides. Nothing is uploaded.
European and Japanese measurement schemes
EN 13402-3:2004, Size designation of clothes — Measurements and intervals, explicitly cited by https://en.wikipedia.org/wiki/EN_13402 . JIS L 4006:1998, Sizing systems for foundation garments, Table 1 cup centres: https://www.normsplash.com/Samples/JIS/122226747/JIS-L-4006-1998-en.pdf . The Japan section of https://en.wikipedia.org/wiki/Bra_size explicitly identifies JIS L4006:1998 for the 5 cm bands and 2.5 cm cups. Accessed / DATA_CHECKED: 2026-10-04.
Common conventions and modern bands
A Bra That Fits community's original published guides: https://www.reddit.com/r/ABraThatFits/wiki/sizing_systems/ and https://www.reddit.com/r/ABraThatFits/wiki/manual_sizing_guide/ . Used for the even-inch modern band rule, inch cup steps, letter sequences and regional band offsets. Only the country-level conventions are used; no retailer or brand-specific table is reproduced. The two-measurement calculation is a simplified starting estimate. Accessed 2026-10-04.
How to use it
- Measure underbust comfortably snug and bust around the fullest point.
- Enter the two measurements and select centimetres or inches.
- Read each system's starting size and check its cup sequence before comparing labels.
Privacy & limitations
Your body measurements are processed only in your browser and are not saved.
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Frequently asked questions
Why do UK and EU results look different?
This tool applies the specified EN-style EU measurement method and the modern UK/US method independently. Commercial conversion charts can encode a different band convention, so the displayed results should not be treated as interchangeable labels.
What about the traditional +4 method?
That method adds 4 inches to an even rounded underbust or 5 to an odd one, then determines the cup using bust minus the resulting band. The calculator displays the modern method without that addition.
Are US and Australian cups standardised?
No. Common US labels include D, DD/E and DDD/F. The selected AU/NZ convention uses single letters after F, while some labels follow UK double letters. Always check the sequence on the item.
Is this a complete fitting assessment?
No. This is a two-measurement starting estimate, not A Bra That Fits' full six-measurement method. Fit varies by brand and style; get measured if unsure.
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