Bra size calculator
The bra size calculator uses your underbust and bust to estimate bra sizes in the US, UK, EU, FR/BE, AU/NZ and JP systems, with sister sizes and a comparison of three methods.
Example result
Example: underbust 30 in, bust 36 in. Enter your own numbers to see your size.
30DDD
US 30DDD, also written 30F · UK 30E
Difference6 in
Same size in other systems
- EU65F
- FR/BE80F
- AU/NZ8E
- JP65G
- JP sizes vary by maker, so read the JP size as a guide.
Sister sizes
- Band down28DDDD
- Band up32DD
- 2 bands up34D
Other published methods give other answers
- Underbust method30DDD
- Add-4 method34B
- EU method, in cm75C
The first two give US and UK sizes, the third an EU size. The methods start from different rules for the band: the underbust method rounds your underbust to the nearest even number of inches, the add-4 method adds 4 inches to it, and the EU method works in centimetres. A different band moves the cup letter too, so the same measurements can give different sizes.
Sizes differ between brands. Use this as a starting point, then measure again and try on.
The calculator takes an underbust and a bust in inches or centimetres. It returns results in six systems, plus sister sizes and a comparison of the underbust method, add-4 method and EU method.
The underbust method rounds the underbust to the nearest even number of inches, with an exact odd whole number going up. Its cup comes from the bust minus that band, rounded to whole inches. The add-4 method is an older rule on some charts: it rounds the underbust to the nearest whole inch, then adds 4 to an even number or 5 to an odd number. The EU method rounds the underbust to the nearest 5 cm and uses the difference in centimetres for its cup letter, from AA at 10 cm to H at 28 cm, moving up one letter every 2 cm. A boundary value takes the higher letter.
Published charts disagree about rounding and band rules. For an underbust of 28 in (71.1 cm), the underbust method gives band 28, the add-4 method gives band 32, and the EU method gives EU band 70. A label chart pairs EU band 70 with band 32. The EU method gives EU and FR/BE sizes only.
The worked example uses an underbust of 30 in (76.2 cm) and a bust of 36 in (91.4 cm). The underbust method gives band 30 with a difference of 6 in: US 30DDD/F, UK 30E, EU 65F, FR/BE 80F, AU/NZ 8E and JP 65G. The add-4 method gives band 34 with a difference of 2 in: US and UK 34B, EU 75B, FR/BE 90B, AU/NZ 12B and JP 75C. The EU method gives EU band 75 with a difference of 16.4 cm, plus EU 75C and FR/BE 90C.
Methods and rounding differ between published charts, and JP letters vary by brand. A calculated size is a point to begin from, so people measure again and try on.
Where next
Look at the whole chart, learn how to measure, or see the sizes of one system.
Bra size calculator questions
How is a bra size worked out from measurements?
The band comes from your underbust and the cup from the difference between your bust and the band. The underbust method rounds your underbust to the nearest even number of inches for the band, and each whole inch of difference is one cup letter. An underbust of 30 in and a bust of 36 in give band 30 and a difference of 6 in, which is a 30DDD in US sizing.
What is the difference between the underbust method and the add-4 method?
The underbust method takes the band from your underbust. The add-4 method adds 4 inches to it first (5 when the rounded underbust is an odd number) and takes the cup from the larger band. The same measurements of 30 in and 36 in give a 30DDD with the underbust method and a 34B with the add-4 method.
What are sister sizes?
A sister size has the band one step up and the cup one letter down, or the band one step down and the cup one letter up. The sister sizes of a 30DDD are 28DDDD, 32DD, 34D. A size table does not say how a bra fits, so measure again and try on.
Why does the same size look different in the UK, EU or Australia?
Each system writes bands and cups in its own way. A 30DDD in US sizing is a 30E in UK sizing, 65F in EU, 80F in FR/BE, 8E in AU/NZ and 65G in JP. US and UK letters match up to DD and then part ways: DDD in US sizing is E in UK sizing. Where a system has no label for a size, the calculator says not listed.
Can I enter my measurements in centimetres?
Yes, switch the unit to cm. The calculator accepts an underbust from 50 to 150 cm and a bust from 50 to 230 cm, and converts at 2.54 cm to the inch. 76 cm under and 91 cm around give a 30DDD.