This means measuring the fullest part of the chest. The measuring tape is placed as tightly as possible on top of the breasts while care should be taken not to depress them or change their shape. The arms should be relaxed and placed on the sides of the body.
To have an accurate reading, you have to place the tape around the torso against the smallest portion of the waist located below the rib cage and just above the belly button.
The measuring tape should be positioned in such a way that it will cover the hips at the widest part when bending a bit to the side.