Six size systems
UK, US, Europe, France, Italy and Australia from the same measurements.
Health & wellness
Bra size calculator
Band and cup from the European EN 13402 method, converted into six size systems, with sister sizes for fitting.
Take your two measurements
The result appears as soon as both measurements are entered. Use a soft tape measure, kept level, over an unpadded bra.
Just under the bust, tape snug, after breathing out.
Around the fullest part of the bust, without pulling tight.
Your estimated size
Starting size
International sizes
- Europe (EU)
- -
- France, Belgium, Spain
- -
- United Kingdom (UK)
- -
- United States (US)
- -
- Italy (IT)
- -
- Australia (AU)
- -
Sister sizes
- Smaller band
- -
- Larger band
- -
The same cup volume with a different band: useful if the band feels too tight or too loose when you try it on.
Method & sources
The calculation follows the European EN 13402 standard: the underbust is rounded to the nearest 5 cm to give the band, and the cup follows the gap between bust and underbust, one cup every 2 cm (about 1 in) from 10 cm (AA). The size is then converted into the other systems.
Formula
EU band = underbust rounded to 5 cm · Cup = (bust − underbust − 10 cm) ÷ 2 cm: AA, A, B, C, D, DD… · UK and US band = 32 + 2 × (EU band − 70) ÷ 5Limitations
- UK, US, Italian and Australian equivalents follow the most common tables; some brands use their own charts.
- The shape of the bust, the stretch and the cut of a bra cannot be read from two measurements.
- The table covers bands 28 to 50 (EU 60 to 115) and cups AA to GG; beyond that, check the manufacturer.
Sources
- ISO 8559-1:2017 - anthropometric definitions for body measurement
- EN 13402 - European size designation of clothes
Was this tool useful?
How does this tool work?
A bra size combines a band and a cup. This calculator works them out from two measurements, your underbust and your bust, using the European method, then gives the matching UK, US, European, French, Italian and Australian sizes, with sister sizes to adjust when trying bras on.
Measure your underbust, tape snug just under the bust, then your bust at the fullest point without pulling tight, in inches or centimetres: your size appears straight away.
The underbust gives the band; the gap between the two measurements gives the cup, one cup size for every 2 cm (about 1 in). For a 28.7 in (73 cm) underbust and a 34.3 in (87 cm) bust, the 14 cm gap gives a B cup: 34B in the UK and US, 75B in Europe.
How to use this tool
Measure your underbust
Standing, arms by your sides, tape level and snug just under the bust.
Measure your bust
Around the fullest part, without squeezing, wearing an unpadded bra.
Read your size and its equivalents
Start fitting with this size, then adjust with sister sizes if needed.
Good to know
Sister sizes
The next band up and down with the matching cup, to adjust when fitting.
Inches or centimetres
Measurements already typed are converted when you switch units.
How a bra size is worked out
Two measurements are enough: the underbust for the band, the gap with the bust for the cup.
European band
underbust rounded to the nearest 5 cm (73 cm → 75)
Cup
bust − underbust: 10–12 cm AA, 12–14 cm A, 14–16 cm B, 16–18 cm C, 18–20 cm D
UK and US band
32 + 2 × (EU band − 70) ÷ 5 (EU 75 → 34)
French band
EU band + 15 (75 → 90)
Equivalents follow the most widespread tables; each brand’s guide is the final word.
Use cases
Know your size before buying
Get a starting size before checking a brand’s guide or ordering online.
Convert a foreign size
Turn a UK size into its US, European, French, Italian or Australian equivalent.
Find a sister size
Keep the same cup volume with another band when a bra feels tight or loose.
Tips and best practices
- Measure in front of a mirror to check the tape stays level across your back.
- When trying a bra on, the band should fit on the loosest hook: it stretches over time.
- If the cup gapes, try the sister size with a smaller band; if it spills over, go up a cup.
Frequently asked questions
How do I calculate my bra size?
Measure your underbust and your bust. The underbust gives the band; the gap between the two gives the cup, one size for about every inch (2 cm): roughly 1 in for an A, 2 in for a B, 3 in for a C, 4 in for a D, 5 in for a DD.
What is the difference between UK and US bra sizes?
The bands are the same. Cups match up to D, then the UK goes DD, E, F, FF while the US goes DD (or E), DDD (or F), G, H. A UK 34E is therefore a US 34DDD or 34F.
How do I convert a European bra size to UK?
The UK band is in inches: EU 70 is a 32, EU 75 a 34, EU 80 a 36. Cups are the same up to D, then EU E becomes DD, F becomes E and G becomes F.
What is a sister size?
A size with about the same cup volume but a different band: go down a band and up a cup, or the other way round. 34B has the sister sizes 32C and 36A.
How do I know if my bra fits?
The band stays level and fits on the loosest hook, the cups hold the breast without wrinkles or spilling, the centre gore touches the breastbone and the straps do not dig into the shoulders.
Why does my size change between brands?
Each brand has its own cut, fabrics and sometimes its own chart. The calculated size is a starting point; the brand’s guide and trying the bra on remain the reference.
Should I measure with or without a bra?
The most reliable way is to wear an unpadded bra, which holds the breasts in their natural position, or to measure on bare skin while standing.
Related tools
Keep going with these tools
Tools similar or complementary to this one.
Similar tools
Calculate your body mass index from height and weight, with adult reference ranges and clearly explained limitations.
Health & wellnessNewFeaturedUse this tool
Calculate your waist-to-hip ratio, place your waist size on the WHO cut-offs and, with your height, get the waist-to-height ratio recommended by NICE.
Health & wellnessNewUse this tool
Find your ideal weight for your height: healthy BMI range and the Devine, Robinson, Miller, Hamwi, Lorentz, Broca, Creff and Monnerot-Dumaine formulas.
Health & wellnessNewFeaturedUse this tool
Read next
GuideBest practicesBeginner
Zakat and Nisab: understanding the 2.5% calculation
Learn how the Nisab threshold, gold and silver standards, net eligible assets and the 2.5% rate fit together - and where a Zakat calculator's assumptions matter.
17 September 20263 min
GuideConcepts and technologiesIntermediate
Working capital, cash conversion cycle and inventory turnover
Understand how working capital, cash conversion cycle and inventory turnover connect when analyzing cash tied up in operations.
25 September 20262 min
GuideConcepts and technologiesBeginner
Hebrew and Gregorian calendars: understand and convert dates
Learn how the lunisolar Hebrew calendar works, why leap years add a month, how nightfall affects the date and how to convert between Hebrew and Gregorian dates.
17 September 20263 min
GuideConcepts and technologiesBeginner
Hijri and Gregorian calendars: how to convert a date
Understand how the lunar Hijri calendar differs from the Gregorian calendar, why calculated dates can vary from local observance, and how to convert both ways.
17 September 20263 min