Clothing Sizes

I'm 5 ft tall and I wear between a 4 and 6 U.S. pant but I have a large chest and usually a med.-large top. I often shop in the petite section in stores like Banana Republic. Will the clothing in Japan be too small for me? Should I prepare myself so I don't get discouraged? Should I not even bother looking at the clothing while I shop there?
From what I'm reading in this forum it sounds like the clothing is very very small.

Contrary to perhaps popular believe, Japanese women come in all shapes and sizes.

And they are all fully clothed!

You may not find something you like at every shop and it's possible some places won't have anything in your size, but you certainly will be able to buy any number of fashionable or cute pieces in any major shopping area.