Tips on Proper Bra Sizing

Most women do not wear the correct bra size. With monthly water retention cycles, dieting, and general aging, it also should not be assumed that the size you were two years ago is the same size you are today (or that a bra can be worn that long, for that matter). Even a change of 5 pounds can change your bra size. This guide will help you to properly measure your bust, so that you can find the size for you.
While most shops will have a salesperson to assist you in proper measurements, in order to buy sexy lingerie from a catalog, it is important to know your size.

How To Know If Your Current Bra Does Not Fit
The back rides up. This may mean that the cups are too small, or the band is too tight. The front of the band is too tight to get a finger under it. This means you need a larger band.
The bra cups should be entirely filled, or you may need a smaller cup. If, on the other hand, the cups are overflowing, you may need a larger cup or a different style of bra.
If the underwire digs in, you may need a larger cup size. (Or your bra could just be very old. In either case, it's time to replace it.) This could also be an indication that the side wings of the bra are not large enough.
Proper Measurements
First, you will need three measurements: under bust, upper bust, and full bust. For under the bust, measure directly under your bust. With all measurements, hold the tape secure but not too tight. For the upper bust, measure above the bust and below the arms.
If the difference between the under and upper bust is less than two inches, the under bust is your band size (round up to nearest even number). If the difference is more than two inches, add 2-3" to the under bust measurement to get an even number and use this as your band size. For the full bust, measure around a fullest part of your breast. Make sure the tape is secure around the back.
Your cup size is determined by your full bust measurement - your upper bust measurement. If the difference is less than 1", you are a AA, 1" is an A, 2" is a B, 3" is a C, 4" is a D, 5" is a DD (or an E), etc.
Beyond Measurements
Of course, your measurements are just the beginning. There are other things to keep in mind when looking for a comfortable, yet sexy bra.
When trying on different bras, make sure that the area in between the two cups actually comes into contact with your chest. Do not make the straps support your breast alone! This will be very uncomfortable over long periods of time, the bra will wear out quickly, and the pressure on the straps can cause back problems.
If you are finding the band sizes to differ for a different brand, you may also need to change your cup size. Generally, as you decrease the band size, you will need to increase your cup size, while a larger band will call for a smaller cup.