To determine your bra size, measure the circumference of the chest in two ways: under the breast and down the center of the chest. To measure the girth of brisket stand up straight and exhale. The tape should encircle the chest tight enough, but not tight – and to be strictly parallel to the floor. Record the resulting figure.
Similarly, measure circumference of chest at nipples. The owners of the big bust in front of this dimension is better to wear well fitting (ideally, pull-up) bra, otherwise the resulting figure may be substantially less than real.
Define the difference between these two volumes. The resulting figure will determine the fullness of the cups. If the difference between the volumes is:

10-11 cm is your size AA (0);

12-13 cm - A (1);

14-15 cm (2);

16-17 cm – s (3);

18-19 cm - D (4);

20-21 cm - DD (5).
For large step sizes is already not two, but three centimeters:

if the difference in volumes 23-25 cm should choose size E (6),

26-28 centimeters (6+).
The number on the label of the bra to the indication of the fullness of the Cup should be equal to your inframammary volume. The step is 5 inches, so if the measurement you got, for example, 76 centimeters – safely increase up to 75.
If you are planning to purchase a linen European manufacturers, it is necessary to consider that in some countries (such as France or Italy) bra size is calculated by a different formula and can be expressed in fractional numbers. For these cases, the difference between the girths should be divided by six. For example, 86-72=14; 14/6=1.6.