There is no way to tell, really, as it varies by manufacturer. It even varies within the manufacturer.
On July 4 I went to buy a pair of shorts, and I was in a big hurry. Such a hurry that I didn’t want to go upstairs, so I went into the junior’s dept., where the clothes are more “young attitude” but I figured I could find a pair of shorts. (This dept. also tends to be cheaper.)
Misses clothes are sized in even numbers, but juniors are odd numbers. I grabbed a 5, which used to be my size. Then I told myself that I hadn’t been in a juniors dept. in 20 years so I also grabbed a 7. Note that I looked at the shorts and the 5 looked within the realm of possibility.
Well, I got the 5 on, but it was tight. I didn’t want tight so I tried the 7.
Couldn’t even get it all the way up.
Wait–it’s supposed to be…bigger. I looked at it again. Same brand. Same style. Same style number. But a larger size. Size sewn into the inside of the waistband so it wasn’t a case of them getting it wrong on the ticket. But they blew it. They got it wrong somewhere along the line, or else the 5 was way off. Or both.
At this point I was out of time so I grabbed a 9, looked it over, and bought it.
It’s huuuuge. I have no idea what happened with the 7.
But this is a not-uncommon shopping experience for women.
Now, online/catalogue places like Land’s End I’ve found to be very reliable. They will have a chart. You match up waist size, bust size, hip size, and the chart will tell you what size to order. According to Land’s End you will wear a size four if your bust measures 33½, your waist measures 27-28, and your hips measure 36½. Other manufacturers will vary but it’s going to be small or extra small.