People ask about re-sizing patterns, so I thought I'd give a little about that here.
The general rule I give in some of the patterns I offer is as follows (this example shows a 1947 Vogue Dress):
To grade a pattern
'With a long straight edge, draw vertical lines down the length of each piece as shown in the accompanying illustration. Make sure each line is drawn to coordinate with the placement of the lines you draw on each adjacent pattern piece (click images below for larger view).
Cut along these lines. Then, take the total difference between the size of this pattern and your size at the bust, natural waistline and low hip (located about 7” below the natural waistline).
For instance, your pattern fits 36” bust, 30” waist and 39” low hip, and you want the pattern to fit a 34” bust, 28” waist and 37” low hip.
Distribute the difference above in the adjustment as follows:
On each pattern piece, take the neck line (center line in orange) in 1/8”, the shoulder length line (middle line in green) in 1/8” and the lines at the side (side line in red) in ¼”.
The adjustments above give a total of 1/2” across the bust, 1/2” across the natural waistline and 1/2” across the low hip per pattern piece. You can take the pattern in along the line you cut by taping the piece you slashed from where you cut the pattern along each line. The adjustment for moving the pattern up in size will be the same process, except one will slash and spread the pattern.
I always recommend making a cheap muslin version of the garment to fit before cutting the final fabric.'
Threads Magazine has an article here for more in-depth reference.