When taking your own measurements, consider wearing a soft cup bra that provides your bust with some support as you will be taking circumferences of your underbust (torso area below your bra band), the widest point of your bust circumference from the apex level, and for cup size, you will do a little math as noted below!
Bust Measurement: (Widest Circumference)
Taking your measuring tape, wrap around the widest point of your bust, keeping it parallel to the floor. Taking this measurement on yourself helps to be standing in front of a mirror, wrap it around your back and let the measuring tape sit level from either of your bust’s apex.
Band Measurement: (The number in your bra size)
With your bra on, take your measuring tape around the bottom band of your bra, making sure your bra straps are at a comfortable length and maintaining the band runs parallel to the floor. This circumference will be your band circumference (or underbust) with the measuring tape being snug to the body. With this measurement, you can round up to the nearest whole number; for even measurements add 4 inches, for odd measurements add 5 inches.
The difference between your bust circumference measurement and your band circumference measurement will determine your cup size. For example, my bust circumference is 38” and my band measurement (underbust) is 34 inches. Below find a chart with the differences and how they correspond to your cup size. This results in 34C.
In intimate apparel/lingerie design, when distinguishing measurements, you are able to go between sizes using the following formula: one band size larger and down in one cup size.
For example: if 34C fits too big in the cup, you can use the alternative of 36B. This typically works when buying bras from different brands, as they are all designed from a starting point/fit model chosen by the brand. This is why bras may fit differently when purchased from different designers.