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I don’t think there is any general size you can go by, every store and manufacturer seems to use a different standard.
For pants, it may be the same as dresses or it might be different, depending on whether your bust-to-hip ratio is the same as the manufacturer’s standard or not.
An online shopping website should have a size chart somewhere on the site with a table of actual measurements showing how the measurements correspond to their sizes. Also, if you already have some clothing from that brand, you can use it as a guide.