Commercial patterns for the home sewist give a list of measurements on the envelope flap. This is where you discover you may be a size 4 off-the-rack but you're maybe a 10 or 12 in sewing patterns. However, those numbers on the flap are not the measurements of the final garment.
You see, patterns are built with ease. Commercial pattern exceptions are corsets and knit, fitted garments. Manufacturers give wearers an extra three or four inches of room in the garment for a few reasons.
First, you want to be able to get into and out of the garment without the aid of a lubricant or pair of pliers. Let's not forget that scene in Dazed and Confused when the young lady had to lie flat on her bed to close her zipper.
Second, our measurements fluctuate on a daily basis. Last night's cheeseburger may hang out in your tummy area today, but a day of salads mean you have a half inch more space to get into your outfit.
Finally, human beings are vain and numbers can seem like a big deal. We get so hung up on measurements indicating one's value-- height, weight, bra size, hip width. That garment ease really does help one save face with oneself when they fib a little on the number.
If you select a commercial pattern, your garment will have ease. Don't expect it to be a second skin unless you tailor it that way.