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Mostly you need to make sure the bra fits comfortably. According to the organization Kids Health, it will not affect the growth of breast tissue if the size is large or small, but it will lead to discomfort during the day. To ensure that your bra fits properly, follow the instructions below for proper bra fitting.
How to Calculate Bra size:
Step 1: Measure Your Band Size

Firstly, Stand straight and measure around your rib cage, just under your bust. Make sure the tape is snug, but not too tight, and round to the nearest whole number#1.
Step 2: Measure Your Bust Size

Secondly, Stand in front of the mirror in a non-padded bra. Enclose the tape measure around your back, under your arms and around the entire part of your bust. Make sure the tape is snug against your skin and level all the way around. Round to the nearest whole number #2.
Step 3: Calculate Your Cup Size

Cup sizes are calculated between your band size and the fullest part of your boobs (the measurements you just took). Check it out:
0″ = AA
1″ = A
2″ = B
3″ = C
4″ = D
5″ = DD
etc.
for example, if your band measures 30″ and the fullest point of your bust measures 32″, there is a difference of 2″. This means you are a B cup.
Step 4: Finalize Your Band Size
To find your band size, take measurement step #1 – rib cage and add another 4 to it. For example, a 30 would be a band size of 34. Add them together and the sample bra size is a 34B. This is how you find out your bra size.
Use a bra size chart:
Look up your calculated bra size in a bra size chart to determine your final size.

Deduct your band size from your bust size. Each inch of difference corresponds to a bra cup size. For example, a 1 inch difference is an A cup, 2 inch difference is a B cup, and in like manner.

Bra sizing international-

Finding the perfect fit in bra?
The right bra will make you feel supported without the pain. According to an expert, there are five specific areas you can always check to make sure your bra fits properly-
1) Your Band 2) Straps 3) Cups 4) Underwire and 5) Center gore
