STEP (1) BAND SIZE
Measure across the bottom of your band, directly under the bust and across your ribcage. Make sure to keep your measuring tape straight around the back to front. The tape should be snug, not tight. If you get an odd number or half number, round up to the next whole number to get your band size. Whatever number you get here, in almost all cases will need to be rounded up to the nearest even number. So if the measurement is 33 than you would just round up to 34. Very easy. But there is one exception to this rule. If you measure 34 1/4 or even 34 1/2, you should round down to 34 instead. The reason for this is simple. Bras lose elasticity every time you wear them so the fit will only get less and less supportive the longer you wear the bra. So when you first purchase a bra it needs to feel snug but not too tight on the LOOSEST hook.
For this example, the band is 34.
This is where it gets tricky...if you already have a bra on and everything is in the cup and it’s comfortable, you’re done. If not, then let’s continue. Here's how to do it. Measure across your nipples at the widest part of your breasts. If the number falls betweens two numbers, then round up to the.
For example, if you measure 41 1/2 then round up to 42.
STEP (3) CUP SIZE
Now take the number from STEP (1) and subtract the number from STEP (2). This gives you the cup size to go along with the band size that was determined earlier. The band size we had earlier was 34 and the bust measurement is 42. Heres the math: Breast (42) - Band (34) = Cup Size (8"). Every inch equals a cup. In this example, 8" is an H cup.
For example, the bra size is 34H.
NO TWO BRAS ARE ALIKE
Since there is no universal sizing for bras, you may be a 34H in one brand and a 36G or 32I in another one. Our suggestion, try on different brands noting the size you are. It will make shopping a little easier. Below is a chart to help you check your math.