Bra Size Conversion Table
| US | UK | EU | FR |
|---|---|---|---|
| 32B | 32B | 70B | 85B |
| 32D | 32D | 70D | 85D |
| 32DD | 32E | 70E | 85E |
| 34B | 34B | 75B | 90B |
| 34C | 34C | 75C | 90C |
| 34DD | 34E | 75E | 90E |
| 36B | 36B | 80B | 95B |
| 36D | 36D | 80D | 95D |
| 38C | 38C | 85C | 100C |
| 38DD | 38E | 85E | 100E |
A bra size is two independent numbers wearing one label: the band (your underbust in inches, rounded to the nearest even number) and the cup (the difference between bust and underbust, one letter per inch). The table below converts that label across the four systems - US, UK, EU and FR - and the converter computes your sister sizes: the neighboring band-cup pairs that hold the same cup volume.
Bottom line: 34B, 32C and 36A are the same cup - go down one band size and up one cup letter (or the reverse) and the breast volume is identical, because cup size is proportional, not absolute: a B cup on a 36 band holds more breast than a B on a 32. This is the entire 'sister size' trick, and it is also why a bra that gaps or digs is often a band problem wearing a cup costume - 8 in 10 women wear bands too loose, which shifts every cup reading off by a letter or two.
The honest part: cup letters diverge between systems exactly where most people get lost - a US DD is a UK E, and a US DDD (also sold as E or F depending on the brand) is a UK F - while EU and FR band numbers switch to centimeters (75 = 34, 90 = FR's 42-free scale). The table keeps the four columns straight; the fitting room keeps the final vote.
How to use
- Measure underbust snug (band) and bust at the fullest point (cup), both in inches, standing straight without padding.
- Enter band and cup into the converter for the full conversion across US, UK, EU and FR - plus both sister sizes.
- Try the sister size when the band is right but the cup wrinkles or spills: same volume, different band leverage.
Frequently asked questions
What are sister sizes and how do they work?
Sister sizes are band-cup pairs with identical cup volume: going down one band size (2 inches) and up one cup letter preserves the volume, and so does the reverse - 34B, 32C and 36A all hold the same breast tissue. The mechanism is proportion: a cup letter means 'difference from band', so a smaller band makes the same letter shallower. Practically, sister sizes are the escape hatch when a brand's band runs loose (sister down for a snugger band) or the cup is right but the band is unavailable.
Why do US and UK cup letters stop matching?
The two systems agree through D, then diverge: the US doubles letters (DD, DDD) while the UK continues the alphabet (E, F, FF, G) - so a US DD is a UK E, and a US DDD is a UK F. Buying British brands (Freya, Panache) with a US letter silently sizes you wrong at the fuller end, which is exactly where the difference matters most. The EU system runs its own letter ladder after E as well (F, G...), and FR follows EU with a band offset of 15.
How do I measure band and bust correctly?
Band: measure underbust snug - tape flat, exhale, no stretching - and round to the nearest even number; that is the band. Cup: measure bust at the fullest point without compressing, subtract the underbust, and each inch of difference is one cup letter (1 inch A, 2 inches B, 3 C, 4 D, 5 DD). Measure braless or in a thin unpadded bra, and re-check after any weight change of 10 pounds or more - bands are the number most people wear too big, and the error cascades into the cup.
Do UK and EU band numbers convert directly?
Yes, and they are the easy part: EU band = underbust in centimeters rounded (32 = 70, 34 = 75, 36 = 80, 38 = 85), and FR adds 15 to the EU number (85, 90, 95...). The letters are where systems fight - always convert the cup through a table like the one above rather than assuming the same letter means the same thing, because a 'C' carries four different volumes depending on which side of the Atlantic the label was printed.