Different companies don't use the exact same measurements for dresses, but this chart should give you an idea. You are not likely to be a perfect match for any given size, so it's best to choose the bust size unless the dress is meant to be tight in the hips... in that case you would choose the dress size that fits your largest measurement. For example, if your measurements were 35-25-39 you would normally buy the size 6, but if it was a tight/ridgid dress you would buy the size 8 or 10 and then have the bust part taken in.