What's The Go With Clothing Sizes?

I am totally over trying to guess what size I am.
Yesterday I went shopping for some cheap work clothes and I mean really cheap, $15 for two Polo shirts.
Now I would usually say that I am a size 14, only since I lost my weight, but here I was buying a 2XL T/shirt. The only reason I even looked at this size was because that was all there was left.
I held it up and measured it around my bust and I thought ooh my god this is going to fit.
When I got it home and tried it on, shock horror, it actually was a firm fit.

Now we all know where it was made, I really don't have to say, but how can anyone really say that they are a size 10,12 or 16 or whatever. the sizes are all over the place.
I would take a 2XL as being a size 20 or more. Why is there not a regulation on measurements for each size.
I measured this T/shirt against a size 14 that I already had at home and it was slightly bigger, I mean about a half centimeter, wow, not what you would expect.

So I have decided that size does not matter, it means nothing. I am going to try clothing on before I even think about the size of it.