How to measure your bra size

Things You'll Need:

* A measuring tape
* Some patience

1. Stand upright with your arms at your sides and be in a relaxed position breathing normally.

2. The band size / chest size is the circumference either above or below your breasts. Both measurements are commonly used for determining the correct size.

3. Upper chest band size - Place the tape around your back and upper chest by going above your breasts and under your armpits. Make sure the tape measure lies taut against your skin. If you get an odd number or a fraction, round up to the nearest even number. For instance, 31.6 inches (80.3 cm) will become 32 inches (81.3 cm). This measurement in inches is your band size.

4. Place the tape measure tightly around your back, going under your breasts and across your ribcage. Add four inches (10.2 cm) if you get an even number and five inches (12.7 cm) if you get an odd number. For example, 28 inches (71.1 cm) will become 32 inches (81.3 cm). This is your band size.

5. Measure your cup size - First measure the diameter of your chest, including your breasts at their fullest part. This part is usually at the nipple level. To determine your cup size, subtract your band size from your chest plus breast measurement. Hence, if your chest and breast measurement is 34 inches (86.4 cm), and your band size is 32 inches (81.3 cm), you will get a difference of two inches (5.1 cm). The table below lists the various cup sizes based on the length of the difference.
6. Difference: Cup Size
1 inch (2.5 cm): A
2 inches (5.1 cm): B
3 inches (7.6 cm): C
4 inches (10.2 cm): D
5 inches (12.7 cm): DD or E
6 inches (15.2 cm): F
7 inches (17.8 cm): G
7.Since you have a difference of 2 inches (5.1 cm) in this example, your cup size is B. From steps 2 and 3, you already know your bra size, which is 32B.

Source - http://www.ehow.com/how_2323135_measure-bra-size.html