How to Measure Bra Size
Find your perfect fit at home in 4 easy steps
⚡Quick Answer
Measure your **band size** snugly under the bust and your **bust size** loosely at the fullest point, then subtract to find your cup letter. Try the bra on to confirm the fit — numbers alone don't guarantee comfort.
Step-by-Step Guide
Measure Your Band Size
Wrap a tape measure snugly around your ribcage directly under your bust, keeping it level all the way around. Note the number in inches and round up to the nearest even number — this is your band size (e.g., 34, 36, 38).
Measure Your Bust Size
Wrap the tape loosely around the fullest part of your chest — typically across the nipple line — and round to the nearest whole number. Make sure the tape is not twisted and lies flat against your back for an accurate bust measurement.
Calculate Your Cup Size
Subtract your band measurement from your bust measurement — the difference in inches tells you your cup letter (1"=A, 2"=B, 3"=C, 4"=D, 5"=DD/E). For example, a 36" band and a 39" bust gives a 3" difference, meaning your size is 36C.
Try On and Adjust
Put on the bra and check that the band sits flat across your back without riding up, the center gore (the piece between the cups) lies flush against your sternum, and the cups contain all breast tissue with no gaps, wrinkling, or spillage over the top. If the band rides up, go down a band size; if cups overflow, go up a cup size — and remember that sister sizes (e.g., 34C and 36B) have the same cup volume.
Frequently Asked Questions
What if my measurement is an odd number?
Round up to the next even number for your band size — for example, a 33" ribcage measurement becomes a 34 band. Some brands do offer odd-number bands like 33 or 35, so check the brand's size chart if you consistently find even bands too snug or too loose. A well-fitting band should feel firm but not restrictive, and you should be able to slide two fingers underneath it.
Why does my size vary between brands?
Bra sizing is not globally standardized, so a 34C in one brand may fit very differently from a 34C in another due to variations in cup depth, wire width, and band elasticity. Always try on before buying, and use a brand's specific size chart rather than assuming your usual size will transfer. The concept of **sister sizes** can also help — if a 34C feels right in volume but the band is too tight, try a 36B instead.
How often should I remeasure?
Remeasure after significant **weight changes** (roughly 10 lbs or more), after **pregnancy or breastfeeding**, or at least every 1–2 years even if your weight stays stable. Breast tissue naturally shifts with age and hormonal changes, so the size that fit perfectly two years ago may no longer be accurate. A quick re-measurement takes under five minutes and can prevent discomfort and posture problems caused by an ill-fitting bra.
What are sister sizes and when should I use them?
**Sister sizes** are adjacent bra sizes that have the same cup volume but a different band size — for example, 34C, 36B, and 32D are all sister sizes. If a bra fits perfectly in the cups but the band feels too tight, go up one band size and down one cup letter (e.g., 34C → 36B). Conversely, if the band is comfortable but the cups are slightly large, go down one band size and up one cup letter (e.g., 34C → 32D). This trick is especially useful when shopping brands with limited size ranges.