Things get even more interesting when you start shopping for vintage clothing. Sizes have risen in the last 20 years (heck, the last 10 years!), but even more so if you compare to 50 years ago. One of the favorite "size acceptance" lines thrown around was that Marilyn Monroe was a "size 12" (or 14). The only problem with that argument is that a size 12 or 14 in the 1950s was NOT a size 12 today!
Here's a clip from a 1942 Spiegel's catalog:
I know it's fuzzy, so here's the translation:
Size 12: 30-24-33
Size 14: 32-26-35
Size16: 34-28-37
Size 18: 36-30-39
Size 20: 38-32-41
Size 22: 40-34-43
Can you imagine being a size 20 with a 32-inch waist??
I've never really worried over the number on the tag, though - I learned to sew as a kid, and I've sewn clothes off and on through my life. If you want to see someone flip, hand them a homemade dress and tell them the size - someone who's a size 6 off the rack will be about a 14 in a pattern!
Here's the current Butterick size chart:
SIZE Bust Waist Hip
6 30 1/2 23 32 1/2
8 31 1/2 24 33 1/2
10 32 1/2 25 34 1/2
12 34 26 1/2 36
14 36 28 38
16 38 30 40
18 40 32 42
20 42 34 44
22 44 37 46
24 46 39 48
Supposedly sewing sizes are closer to what historical sizes were, but even they have shifted in recent years. The numbers here are definitely larger than the 1940s ones.
At the end of the day, it doesn't really matter, other than it creates screwy numbers when we consider that a size 12 50 years ago is what? A size 2 or 0 now?