An estimated of between 75% to 80% of women do not know their proper bra measurements. Without knowing these measurements, it can be very difficult to buy fashionable and well fitting clothes. Many women's clothing items use bra or cup size measurements to distinguish differences in fit, so these measurements can be extremely important. This section will arm you with the knowledge you need for these crucial measurements. Additionally, a woman's breasts change significantly over time, particularly during and after pregnancy. Weight loss, gain and monthly cycle variations can also have an effect on the fit of your bra. It is advised that you check your bra size once or twice ayear or as necessary due to significant weight changes. Before you begin:    

• Try to get someone to take the measurements for you - your posture will be more relaxed and natural. The measurements should be more accurate.
• Stand up straight and breathe normally
• Don't measure over the top of clothing
• Wear the bra you feel most comfortable in

Use a cloth tape measure if possible. Note: Older flexible tape measures can sometimes stretch and distort over time. Traditional measurement method:    Determining your Bra/Band size
(ribcage circumference measurement)

 1.                  Measure around the chest directly under the breast at a constant height with the cloth measuring tape. Add 5 inches to that measurement. This dimension is your bra/band size (If the bra size works out to an ODD number go up one inch to the next EVEN number.) This should equal the circumference around the chest, directly above the breasts/under the arms. 

2.                  Now measure around the chest at the height of the fullest part of the breast including that of the nipples. The measuring tape should be held horizontal, flat on your back, and your arms should be down. Make a note of that measurement (only used for comparison) and compare it to the Bra Size from step 1.  

3.                  To determine the proper Cup Size, find the difference between step 2 and step 1 (step 2 minus step 1.) Use the chart below to determine your Cup Size.

Chart to Determine Bra Cup Size 

1 inch ~= 2.5 centimeters 

Example:

Step 1: Underbust measurement is 37". Add 5 inches. Bra Size is 42.
Step 2: Full bust measurement is 45".
Step 3: 45 - 42 = 3" difference. Cup size is C.
Result: Buy a 42C bra.  

This measurement guide is but an approximate guideline. Each person is unique, of different build and frame, and naturally all busts differ in volume, shape and spacing, just as each person's unique body size, height, and weight that has an affect on a bra's fit. Additionally, bra size alters according to changes in your body due to factors such as exercise, pregnancy, diet, aging or even water retention. A tape measure and simple formula may not always tell the whole story.

Plus, even if the measurements ARE accurate, there are no real "standards" for bra sizing as we can spot from the many differences commonly seen amongst manufacturers.  If a bra in your size does not fit you, first try to adjust the bra straps or band hooks before opting for a bra in another size. If, after proper adjustments are made, the bra still does not fit well, then follow what your body is telling you. Above all else, it is very important to choose comfort and a good fit rather than restricting yourself to your bra size. . This is very much like shoe size and a good fitting needs the trying on a few pairs to determine the right design and fit.        

Whereas in the case of most European countries, sizing is seem done in Metric with a letter cup size. However, this is again not the same for all countries in Europe, such as in Italy where a different system is being employed. In Australia, a totally different system of which is based on the dress sizing charts is used.

The chart below gives a general comparison of the sizes that can be used as a general reference when purchasing lingerie that are made in different countries.