I can pretty much guarantee that it’s the wrong size. Either that or it’s so hopelessly worn out that it should be in the garbage, not on your body. The chart below is the most informative one I’ve found showing just how bra sizes actually work.
5 Tips to Find Your Perfect Bra Size
I struggled to find a properly fitting bra from the time I was a senior in high school until I was about 24. It wasn’t until I did some research online and found a UK based store called Bravissimo that I learned how to find a bra that fit me correctly. The most common problem that I had was that even if I wasn’t spilling over the cups, the underwires were pinching in the middle. The solution is not to go up a band size if the cups are too small like the bra-fitters in the mall had been trying to get me to do. You do not want the band to be too loose or your boobs will spill out underneath or will be too heavy and push down in the front, causing the straps to dig in to your shoulders and making the bra ride up in the back.
The best way to start out is to look in the mirror and see how your current bra is fitting and adjust your sizing from there. If you absolutely have to measure to find a good point to start from, HerRoom.com has a good measurement calculator. Just remember that the measurement is only a starting off point and you will only be able to tell your perfect bra size by the way it fits and feels.
One more thing. What may be your perfect size in one brand, may not be in another, so be sure to test all new bras. Don’t just assume you will always be the same size across the board in all brands/styles.