Over my years of blogging, I have had a number of inquiries about how I do my pattern sizing (or rather, pattern re-sizing), to take a vintage pattern that is too large or too small for my measurements, and make it fit.
The most accurate method is the cut-and-spread method, where the pattern pieces are traced, slashed, and carefully, mathematically spread or overlapped in just the right way to make all the dimensions larger or smaller as needed. (A good tutorial for this method can be found here.)
However, as I have frequently stated on the blog, I am Not A Perfectionist, and that method is way too time consuming for me. I prefer a less accurate and much faster way, which I will show you here. I have used this for every pattern I have resized during years of sewing garments - most of the time with quite good results.
This method works best for only sizing up or down one size, but it can be used successfully for skipping multiple sizes with more care and trial-and-error.
Not every pattern works for this, however. You need one with a relatively simple back. My green plaid dress, for instance, would not work very well to resize because all those dart tucks on the bodice would need re-spaced, unless you added or subtracted exactly the right amount of fabric to take out or add one dart tuck.
Here are some more examples of patterns which do not work well for resizing without a lot more thought and work. The first one has evenly spaced darts and seams the whole way around the skirt. The second one also has a skirt yoke with evenly spaced points the whole way around.
Here are examples of patterns that are easy to resize. This one is very basic, with one back bodice piece (potentially a collar piece if you do the view with a collar) and one back skirt piece, all on the fold:
This one is also easy, though not quite so intuitive. It has a back bodice piece on the fold and a center back skirt seam.
This one has more pieces, but as you can see, it is still easy since most of the back pieces - yoke, collar, bodice, and inset belt - are on the fold, while there is a center back seam on the skirt.
Resizing One Size Different
Ok, now. To size a pattern up two inches or one size, first look at your pattern instructions. Many of these old patterns have what they call "let out seams" which are deep seam allowances on the side seams. That may be all you need - if you sew a 3/4 inch seam allowance only 1/4 inch deep on each side, for example, that gives you your extra two inches right there.
If the let out seams are not a feature, or you need more than the extra room they provide, first look at the back sketch, which might be on the front or the back of the pattern envelope. If the back pieces (including facing) are to be cut on the fold, I simply lay each of them one inch off the fold. One inch doubled makes 2 inches added.
To size a pattern down, I will lay each piece one inch overlapping the fold, which takes 2 inches out of the center back skirt and bodice.
Please note: I have not noticed any difference with dart placement on the front by doing this. Usually the difference between the dart placement for one size is very slight, which you can tell if you look at a modern multi-size pattern, and I have not had any problems with the front fit by adding or taking out 2 inches of fabric in the back. So I usually let all other pieces untouched when resizing one size up or down.
If one or both back pieces have a seam down the center, to size it up I simply add an inch to the center back seam. You can either measure and mark it, or just eyeball it as you cut if you trust yourself. So I would cut where my finger is, instead of where the edge of the pattern is. Make sure you pay attention to which is the center back seam for the skirt pieces, though, so you aren't adding it to the back side seams instead!
Many patterns have a back bodice piece on the fold and a center back skirt seam, like some of the examples above. I would lay the back bodice piece (and facing) off the fold and cut the center back skirt seam an inch away from the edge of the pattern. To size it down, I would overlap the back bodice piece on the fold, and trim the center back skirt seam an inch narrower - where my finger is, on the photo below. The best way to do this is to cut and mark the other 3 sides of the skirt piece, then unpin the pattern piece and move it over one inch to cut the last seam - that way all your markings for that edge are also moved over and you get an accurate flare or curve.
Adding or taking away the same amount from all center back piece means that your darts and skirt seams should still match up - there is simply less or more fabric back there.
Keep in mind that ALL the back seams need to be the same, whether you are adding or subtracting. So if you have a pattern with an extended collar that meets in the back like this one, the collar seam on the FRONT bodice also needs to be added to or trimmed off - both on the front bodice piece and on the facing piece.
I admit I often forget this one, and like for my gray rayon dress, ended up piecing the bodice collar and recutting the facing since that is on the top and is the piece you see when the collar is finished.
If you have a Peter Pan collar, or some other type of collar that is not on the fold when the bodice is, you have to add the same amount to the back of the collar as you did to the fold of the bodice. Again, I usually cut part of it, then move the collar down an inch and finish cutting it; that way the curve remains correct.
In a nutshell, all additions or subtractions need to be the same, for all the back pieces. Just take some time to look over the pattern and recognize how many pieces need altered, and which ones need it on the seam and which on the fold. Usually at a minimum it will be bodice, back center skirt, and back facing (unless you are just using a bias facing strip, which you would simply cut a little longer).
Resizing Bigger Differences
Now, things get more complicated when you are sizing up several sizes, like doing a size 12 pattern for a size 16 or 18 measurements, like this 1940s summer suit I did last year.
As a general rule of thumb, I will not add or subtract more than 3 inches total to the center back. This means that if I need to size a pattern up 4 inches, I will lay the pattern pieces 1 1/2 inches off the fold (1 1/2 inches doubled adds 3 inches total) or cutting 1 1/2 inches away from center back seams, and add 1/2 inch to the side seams when I am cutting it out. This would include bodice side seams, skirt side seams, and sleeve side seams. Also cuff side seams if the pattern has them.
To size it down, I reverse the process, laying the pattern pieces 1 1/2 inches overlapping the fold (or trimming from center back seams), and trimming 1/2 inch from all the side seams.
If I am sizing up more than 4 inches, I will add up to 3 inches to the center back as previously described, then split the remaining inches and add that to the side seams. But the bigger the resizing, the riskier the fit is, and by this time there often is a significant difference in bust dart placement on the front, so it's best to do a trial version or a muslin before cutting into your fashion fabric.
For my 1940s summer suit, I actually added too much fabric in, and had to add a 2nd dart to each side of the back to make it fit me. That worked since it was a jacket and didn't necessarily need to match up with skirt back seams like a dress might. But that's a risk when winging it to this extent without a muslin.
Also, altering a pattern 4 inches or more can create fit issues at the neck, sleeve tightness, and bust/waist ratio. My adjustable house dress here has fit issues at the neck since I took out too much of the yoke and back and didn't do a muslin first. If I do this pattern again, I will trim more off the side seams and take less out of the back yoke and center back panel.
This one I sized up about 6 inches, and it has sleeves that are a tad too tight for comfort since I didn't add quite enough on to them when cutting them out. Thankfully it is still wearable. Also it has interesting 2 part sleeve construction, which made me study which even were the right seams to add to the seam allowance!
I do generally have no issues at all when resizing only one size up or down, and that alone gives you a lot more freedom when buying patterns. If you are a size 16 for instance, now you can also buy size 14 and size 18, with no qualms. To do more than that requires more trial and error, but still can be done. Plus it is very quick and easy, requiring little extra time when cutting out a pattern, once you've thought through your changes.
Helpful? Clear as January mud? Let me know if you have any questions, or how well it works for you if you try it!
Verity Vintage Studio
