How to Measure Your Bra Size

Two measurements decide your bra size: a snug, level underbust for the band, and a relaxed measurement at the fullest point for the cup. Two minutes, a mirror, and any tape or string. We do not add four inches to anything; your band is your real underbust number.

Step 1: the underbust (your band)

Stand naturally in front of a mirror and wrap the tape around your ribcage directly under your bust, where a band actually sits. Check the mirror: the tape must be level front and back, since a back that drifts up reads small. Pull it snug, the way a supportive band feels, exhale normally, and read the number. In centimeters or inches, whichever your tape speaks; the calculator takes both.

Step 2: the bust (your cup)

Move the tape to the fullest part of your bust, usually across the nipple line. This one stays relaxed: touching skin everywhere, compressing nothing. If tissue is soft and sits low, a second reading leaning forward 90 degrees captures volume the standing tape misses; use a number midway between the two. Read it, and you are done measuring.

Turning numbers into a size

The calculator does the conversion across all 7 systems, but the logic is worth knowing: the band is the underbust rounded to sizing convention, and each inch of difference between bust and band is one cup letter. A 31 inch underbust with a 36 inch bust is a 32 band with about 4 to 5 inches of difference: a 32D to 32DD starting point, whose sister sizes and international equivalents the tool lists automatically.

The mistakes that move sizes most

• Measuring over padding: inflates the cup letter by one or more.
• A drooping back tape: shrinks the band and inflates the letter.
• Loose underbust reading: produces bands that ride up within weeks.
• Holding a deep breath: adds an inch that disappears when you exhale.
• Trusting a years-old size instead of the tape: bodies change; two minutes settles it.