Bra Size Calculator helps you find a comfortable, supportive fit by using two simple measurements: band size and bust size. First, measure snugly around your ribcage, just under the bust, to get the band measurement. Next, measure around the fullest part of the bust while standing naturally. The calculator subtracts the band from the bust to determine the cup size, while the band measurement sets the number. Getting the right size improves posture, comfort, and confidence, and reduces issues like strap slipping or digging wires. Sizes can vary by brand, so results are a starting point. Re-measure every few months, or after growth or weight changes, and try different styles for best support. Use soft tape and breathe normally. Always.