Chest size is probably the most misunderstood measurement of a woman's body. Many women mistakenly believe that chest (bust) size is the same thing as bra size. It isn't. Chest measurements do not take into account the size and shape of the breasts.
Measure the distance around your body just below the breasts as you stand with erect posture.
Add 12.5 cm (5 inches) to this measurement to get your chest size. Even though it doesn't make a lot of sense, adding the 12.5 cm will give you an accurate measurement. This is your bra size.
Determine your cup size by measuring your bust (without a bra on) at the fullest point. Subtract your chest size from this measurement. Refer to a chart of cup sizes and locate the cup size that matches this measurement (see the Resources section). Generally cup sizes are indicated in whole cm or whole inches. If your measurements are right on the edge of two sizes, you may need to try both to see which fits best. This new bra size may be different from what you have always worn and may seem inaccurate to you, but it is accurate. Many women discover that their usual size changes in either band size or cup size and are surprised at how much better a new bra fits once they have determined the correct size.
Measure at the fullest point of the bust while wearing a good support bra to determine your chest/bust size. You will need this measurement to purchase clothing that fits properly. This number will be larger than your bra size, but is what determines the fullness of clothing in the bust area.
Keep in mind that knowing your correct bra size will provide you with well fitted undergarments that will flatter your natural shape and size. Knowing your bust size (the number of centimetres around your bust) will make it easier to purchase clothing that fits well.
Sewing clothing that fits well requires accurate measurements.
Avoid the temptation to suck in to get a smaller measurements. Although it may make you feel better to think you wear a smaller size, your clothing will not fit well and you will not look as good as you would in properly fitted undergarments and clothing.
Always measure so that the dressmaker's tape is taut, but resist the urge to secure the measure too tight. This will result in inaccurate measurements and clothing that is too small for your build.