Many women do not wear the correct bra size. Bras should fit comfortably snug with the band flat across the back and the breasts are fully supported and are not spilling out of the cups. Wires should not be digging in and the wire between the breasts should lay flat. Proper-fitting bras should not be painful or uncomfortable.
Put on your most comfortable bra. With the measuring tape, measure around the bra directly under the bust after exhaling—this measurement should be the smallest possible. You can have a friend take down the measurement or hold the measuring tape. Round all fractions up.
Add 4 inches to the under bust measurement if the measurement is even. Add 5 inches if the measurement is odd. For example, if your under bust is 28 inches, your band size is 32 and if it is 27 inches, your band size is also a 32.
Stand straight with your arms relaxed at your sides and have a friend measure around the fullest part of the bust. Make sure that the tape measure is just touching the apex of the breast and not binding. Round up to the nearest inch as you did to find the band size.
Subtract the band size measurement from the second measurement. The difference is the cup size. If the difference is between 0 to 1/2 inch you have a AA cup; difference of ½ inch to 1 inch is an A cup; a 2-inch difference is a B cup; a 3-inch difference is a C cup; a 4-inch difference is a D cup; a 5-inch difference is an E cup; and a 6-inch difference is an F cup. For example, if your second measurement is 35 inches and your band size is 32, your bra size is a 32C.