How do I measure my bra size?

Two measurements: (1) Band size: measure around your ribcage directly under your bust. Round to the nearest even number (add 1 inch if it's an odd number). This is your band size (32, 34, 36, etc.). (2) Cup size: measure around the fullest part of your bust. Subtract band size from bust measurement. Difference 1 inch = A cup; 2 inches = B; 3 inches = C; 4 inches = D; 5 inches = DD/E. Repeat measurements while wearing a non-padded bra.

What does it mean if a bra fits wrong?

Signs of incorrect bra size: straps digging in (band too big, straps overcompensating); band riding up (band too big); spillage over the top of cups (cup too small); gaping cups (cup too large); center gore not lying flat against the sternum (cup too small). Studies suggest 70–85% of women wear the wrong bra size. The most common error is too large a band and too small a cup — try sister sizes (e.g., go from 36C to 34D: same cup volume, different band).

What are sister sizes in bra sizing?

Sister sizes share the same cup volume with adjacent band sizes. Going up one band size = go down one cup letter. Going down one band size = go up one cup letter. Examples: 34D ↔ 36C ↔ 38B (same cup volume). 36DD ↔ 34E ↔ 38D. Sister sizes are useful when your measured size isn't available, or when a different band-to-cup balance is more comfortable.

Bra Size Calculator

Bra Size Calculator — How to Measure & Convert

Finding the right bra size requires two measurements: your underbust (band size) and your bust (cup size). This calculator converts your centimetre measurements into US, UK, EU, and FR/BE bra sizes.

How to measure

Underbust (band): Wrap a tape measure around your ribcage directly under your breasts. Breathe normally. The tape should be snug but not tight.
Bust: Measure around the fullest part of your bust, keeping the tape parallel to the ground.

Band size calculation

Convert underbust cm to inches: cm ÷ 2.54
Round up to the nearest even number in inches — this is your US/UK band size
EU band = underbust cm + 15 (rounded to nearest 5)
FR/BE band = EU band + 15

Cup size from bust–band difference (US/UK)

Difference (inches)	US Cup	EU Cup
≤0	AA	AA
½	A	A
1½	B	B
2½	C	C
3½	D	D
4½	DD	E
5½	DDD/E	F
6½	F/G	G

Sister sizes

Sister sizes have the same cup volume but different band sizes. For example, 34C = 36B = 32D. If your band size doesn't feel right, try a sister size.

References

Greenbaum AR et al. (2003). "Breast measurement and sizing: a systematic review." Aesthetic Plast Surg 27:403–408.
Mason BR, Page KA, Fallon K (1999). "An analysis of movement and discomfort of the female breast during exercise." J Sci Med Sport 2(2):134–144.

How Bra Sizing Systems Differ

Bra sizing is inconsistent across countries and brands. The US and UK use inch-based band sizes (32, 34, 36…) but different cup scales. Europe uses centimetre-based bands (70, 75, 80…). France and Spain use a different centimetre scale starting 15 units higher. A US 34C, UK 34C, EU 75C, and FR 90C all refer to very similar (but not identical) fits. Always measure yourself freshly before buying online and consult the brand's specific size chart.

International Bra Size Conversion

US	UK	EU	FR	AU
32	32	70	85	10
34	34	75	90	12
36	36	80	95	14

How Bra Sizing Works

Bra sizing combines two measurements: band size (the circumference of the ribcage just below the bust) and cup size (the difference between the bust circumference at its fullest point and the band size). In the US system, each inch of difference between bust and band corresponds to one cup letter: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, and so on. Band sizes are even numbers (32, 34, 36, 38, 40) and are derived by measuring in inches and rounding to the nearest even number.

Sister sizing is the concept that adjacent band sizes with the same cup volume exist. A 34C has the same cup volume as a 32D (one band size smaller, one cup larger) and a 36B (one band larger, one cup smaller). This matters when a preferred band size is unavailable — the cup volume remains equal.