Find Your Bra Size
Grab a soft measuring tape and measure in a well-fitting, non-padded bra or none at all. Tap ? icons for help with any term.
Band size
Cup size
Bust measurement
Sister sizing
Underwire vs wireless
Band Size The number in your bra size (e.g. 34B). It refers to the circumference of your ribcage just below your bust. A correct band should feel snug but not dig in — you should be able to slide two fingers underneath it. Most of your bra's support (about 80%) comes from the band, not the straps.
Cup Size The letter in your bra size (e.g. 34B). It represents the difference between your underbust and bust measurements. Each inch of difference equals roughly one cup size: 1" = A, 2" = B, 3" = C, 4" = D, and so on. Cup size is always relative to the band — a 34C and 36B hold the same volume of breast tissue.
Bust Measurement This is the measurement around the fullest part of your chest — usually across the nipple line. Keep the tape parallel to the floor and don't pull it tight; it should sit gently against your skin. Measure while wearing a non-padded bra or no bra at all for the most accurate result.
Sister Sizing Sister sizes share the same cup volume but have different band sizes. For example, 32D, 34C, and 36B all contain the same cup volume — just on different band widths. If your bra fits perfectly in the cup but the band is too tight, go up one band size and down one cup letter (e.g. 34C → 36B). If the band is too loose, do the opposite.
Underwire vs Wireless Underwire bras have a thin wire sewn into the base of each cup that follows the natural curve of your breast. They provide more lift and definition. Wireless (or wire-free) bras use structured fabric instead and are generally more comfortable for everyday wear. For accurate size calculation, measure without a heavily padded bra.
1
Band (underbust)
Measure snugly around your ribcage, directly under your bust. Breathe out normally.
2
Bust (fullest point)
Measure loosely around the fullest part of your chest. Keep tape parallel to the floor.
Your bra size across sizing systems:
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Convert Your Bra Size
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Your size in every system:
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Common Questions
Why do I wear different sizes in different brands?
Every brand uses slightly different block patterns and grading systems. A 34B in one brand may fit like a 34C in another. Always refer to the brand's own size guide and measure yourself before purchasing.
What's the difference between US and UK bra sizing?
The band numbers are the same between US and UK, but the cup letters differ starting from DD. In US sizing, DD is followed by DDD (or F), while UK sizing uses E, F, FF, G and so on. So a UK 34E equals a US 34DDD.
Why do EU bra sizes look so different?
EU band sizes are calculated in centimetres and add 15 to the underbust measurement (e.g. a US 34 band = EU 75). The cup letters are similar but start diverging at D. Always use a converter when shopping from European brands like Triumph or Simone Pérèle.
How often should I remeasure my bra size?
Experts recommend measuring every 6–12 months, or whenever your weight changes significantly, after pregnancy, or if your current bras stop feeling comfortable. Up to 80% of women wear the wrong bra size at any given time.
What is sister sizing?
Sister sizes share the same cup volume but use a different band size. For example, 34C, 36B, and 32D all contain the same cup volume. If a bra fits in the cup but not the band, try the sister size up or down.
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