A quick guide on how to properly take your measurements to determine your clothing size! I love this little guide from a 1940s Bella Hess catalog. If you notice dress sizes were based on your bust size, divided by 2, then subtract 2 inches.
So if your bust measured 32", you would be a size 14 in the 1940s. (32/2 - (2)).
Source: Scanned from Bella Hess 1940 Catalog via adore_vintage