Bra Size Calculator
Estimate your bra size in UK, US and EU sizing from two tape measurements.
About the Bra Size Calculator
Band size comes from the underbust measurement; cup size from the difference between bust and underbust. In UK and US sizing each inch of difference is one cup; in EU sizing (EN 13402) each 2 cm is one cup, starting with A at 12–14 cm.
Older methods added 4 or 5 inches to the band. Most fitters now use the measured underbust, which this calculator follows. Treat the result as a starting point: fit varies by brand and style.
The formula
Band = underbust (to nearest even inch); Cup = bust − band
- UK/US cups
- 1 in = A, 2 = B, 3 = C, 4 = D, 5 = DD, …
- EU band
- underbust in cm rounded to the nearest 5
- EU cups
- (bust − underbust): 12–14 cm = A, then +2 cm per cup
How to read your result
- If the band rides up, go down a band and up a cup (sister size).
Worked example
Example: UK size = 36D
- Inputs: Measurements in: Inches; Underbust (snug, round the ribcage): 35; Bust (loosely, at the fullest point): 40.
- Formula: Band = underbust (to nearest even inch); Cup = bust − band
- Result: UK size = 36D
Questions people ask
What is a sister size?
Sizes with the same cup volume: going down one band and up one cup (34B → 32C) keeps the same cup volume.
Are UK and US cup letters the same?
Up to D. After that the UK uses DD, E, F, FF…, while the US uses DD/E, DDD/F, G…