Bra Size Calculator (Cup)
Enter your underbust and bust girth in centimetres; the difference gives your cup letter under the European standard EN 13402-3. You then pick the band number for your underbust girth from the brand’s size chart.
- Bust − underbust difference17 cm
- Difference range of this cup16–18 cm
- Underbust girth (band measurement)74 cm
Cup intervals (EN 13402-3): CEN, EN 13402-3:2004 madde 4.1.3 (s. 10); SIST EN 13402-3:2005 (özdeş kabul) önizlemesi
How it is calculated
EN 13402 is the European Committee for Standardization’s (CEN) standard for size designation of clothes. Under clause 4.1.3 of Part 3 (2004), the size of bras, corsetry and swimwear with cups is set by the underbust girth and the bust girth; the cup is the difference between the two, lettered in 2 cm steps: AA 10–12 cm, A 12–14 cm, B 14–16 cm, C 16–18 cm, D 18–20 cm, E 20–22 cm, F 22–24 cm, G 24–26 cm, H 26–28 cm. The edition in force is EN 13402-3:2017, which Turkey is among the countries bound to implement. The 2017 edition gives its measurement and interval tables only as “examples of best practice” in an informative annex and says companies build their labels from their own measurement tables. So band numbers and cuts can differ between brands; this calculator takes the cup letter from the 2004 table and leaves the band number to the brand’s chart.
Cup difference (cm) = bust girth − underbust girthThe cup letters and their difference intervals in EN 13402-3:2004: AA 10–12 cm, A 12–14 cm, B 14–16 cm, C 16–18 cm, D 18–20 cm, E 20–22 cm, F 22–24 cm, G 24–26 cm, H 26–28 cm. The standard writes the intervals with shared ends; this calculator puts a difference exactly on a boundary in the upper cup and reminds you to try both.- Stand upright and relaxed, in a thin unpadded bra or none.
- Measure the underbust girth just below the breasts, tape parallel to the floor and snug against the skin.
- Measure the bust girth around the fullest part of the bust, tape parallel to the floor, without pulling it tight.
- Subtract the underbust girth from the bust girth and read the cup letter from the interval the difference falls in.
- For the band number, find the size in the brand’s chart whose range covers your underbust girth, and add the cup letter to it.
Example
Underbust 74 cm, bust 91 cm: the difference is 91 − 74 = 17 cm. 17 cm falls in C 16–18 cm, so the cup letter is C. The band number is the size in the brand’s chart that covers 74 cm.
Frequently asked questions
Why does the cup depend on the difference and not on the underbust?
EN 13402-3 defines the cup as the difference between the bust girth and the underbust girth. The same difference gives the same letter at any underbust; a 17 cm difference is a C cup at both 70 and 90 cm underbust.
Why doesn’t the calculator give my band number (e.g. 75)?
The band steps and ranges are in the standard’s size table; the 2017 edition gives such tables only as examples and says companies use their own. We could not check that table at a primary source, so we don’t guess the band: pick the size in the brand’s chart that covers your underbust girth.
My difference is right on a boundary. Which cup should I take?
The standard writes the intervals with shared ends (e.g. 10–12 and 12–14 cm), so exactly 12 cm is the end of both cups. The calculator shows the upper one; trying both is best.
Does it show UK or US sizes too?
No. We found no official conversion table between UK or US sizes and EN 13402 to rely on, so only the EN 13402-3 cup letter is given. When buying in another system, use that brand’s own chart.
When should I measure again?
Measure again whenever your bra no longer fits well or you are unsure of your size. Measure the same way each time (same posture, same tape position) and try bras on before you buy where you can.
Source
- CEN, EN 13402-3:2004 Size designation of clothes – Part 3: Measurements and intervals (adopted identically as SIST EN 13402-3:2005, SIST preview): clause 3.4 (p. 5) cup size definition; clause 3.7 (p. 6) range definition; clause 4.1.3 (p. 10) bra sizes and cup intervals AA 10–12 … H 26–28 cm
- CEN, EN 13402-3:2017 Size designation of clothes – Part 3: Size labelling based on body measurements and intervals (SIST preview): European foreword (p. 3) supersedes the 2013 edition, Turkey among the countries bound to implement it; Introduction (p. 4) values are “examples of best practice”; clause 3.3 (p. 5) cup size definition; clause 4.3 (p. 6) range; clause 5.1 (p. 7) companies use their own measurement tables