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Pattern Sizing Experiment: Part 1 – Grading vs. Ratios

This post was a long time coming. I knew I wanted to try this sizing experiment for more than a year; and over the last 6 months or so, I’ve been trying to work on it in between all my other work and personal projects.

(Warning: this post involves lots of words and math.)

First let’s talk a little about body measurements and standard sewing pattern sizing. Sewing patterns tend to be labeled with larger size numbers than mass produced clothing.

I talked about sewing pattern sizes vs. ready-to-wear size numbers and vanity sizing a couple years back in this post (but that was probably before many of my current readers found my blog).

I’m sure you’ve heard people say that the standard measurements used in the clothing industry have shifted over the decades. But they really haven’t changed as much as people think. The only thing that has really changed is the size number on the label – known commonly as “vanity sizing”. The standard body measurements have barely changed from year to year.

Here’s a section of a spreadsheet of my vintage patterns showing sizing for a 34-inch bust. Notice that the biggest change from year to year is the size number not the measurements used:

Years in italics indicate decade when exact year is unknown.

You’ll see that in the 1940s and ‘50s, a 34-inch bust was considered a size 16 in sewing patterns. In the late 1950s and through the 1960s, that same bust size became a size 14 with a slightly smaller waist and hips. Then in the 1970s, the 34-inch bust became a size 12 while the waist and hips went up a little in proportion – proof that there is a bit of psychological vanity sizing in sewing patterns, but not as drastic as it is in the ready-to-wear industry.

Today’s sewing pattern size 12 is the same as it was in the ‘70s with measurements of 34-26.5-36.

Most patterns are drafted in a mid-range size and then graded down for the smaller sizes and graded up for the larger sizes. This method involves some math and a whole bunch of measuring. (Threads Magazine provides a good explanation of grading here and a quick-guide chart here.)

Now, on to my experiment.

I admit I’m lazy when it comes to grading patterns. The math isn’t complicated, but all that measuring is a lot of work.

I started using my cheater’s method years ago when I needed to increase the size of flower-girl dresses for little girls who were larger than a standard pattern but proportionally still the shape of a standard girls’ pattern. (Part of the reason I started doing this stemmed from last minute clients who didn’t give me the time to do much patterning.)

I compared the differences on the pattern’s standard measurement charts and used ratio computations to find the percentage of the needed size increase. Then I just copied the pattern at the larger percentage on my home printer.

This enlarging method also helped me make a quick bodice pattern for a cousin in my sister’s wedding, who was really tall for her age but still not shaped like a woman yet. So far, this method for enlarging a kid’s pattern has worked for me every time with very few (if any) alterations needed.

When I wanted to sew a vintage pattern for myself but only had it in a size that was 2 or 3 sizes too big, I used my ratio method to shrink it to my size on the copier.

I did this for myself for a few years, getting a nearly perfect fit every time I shrank a pattern. For a long time, I thought vintage patterns were just drafted better, or differently.

But then I discovered that a vintage pattern in my actual size had as many fit issues as most modern sewing patterns. And I began to reexamine why shrinking by a percentage seemed to work better for me.

I think it’s because I am proportionally smaller than the average size used to draft most patterns. (I am small but not petite by clothing standards.) I don’t need merely a few areas changed, or some areas changed more than others (like when grading). I need everything equally shrunken down.

I had decided to test my theory by doing a real comparison of a vintage pattern that I owned in both a bust size 34 and a bust size 31 (my actual size).

I chose the Simplicity 7136 pattern from 1967 for a couple of reasons – I had it in two sizes and it had very basic style-lines, making it easier to compare small differences.

Simplicity 7136 Dress or Beach-dress & Shorts

I made three mockups – one straight from the B31, one straight from the B34, and one B34 copied at 91%.

NOTE: Most vintage patterns have actual stitch lines printed on the pattern pieces. If you are using a pattern without marked seam allowance, you will need to either cut off the seams allowance before copying or make a line to measure what the new copied seam allowance ends up being. You will want to sew on the actual copied stitch lines, so adjustments to seam allowance may be required.

Three mockups or muslins.

Here’s the math I used with the bust measurements printed on the pattern envelope to determine the scale factor:

Bust 1            31
Bust 2           34     =     91%

My theory was that I could also apply this percentage to both of the larger waist and hip measurements to obtain the corresponding chart values:

Waist 2 x 91% = Waist 1:
26 x 91% ≈ 24
 
Hip 2 x 91% = Hip 1:
36 x 91% ≈ 33

I’m obviously rounding to the nearest whole number because that’s the precision on the pattern envelope.  And look!  It’s pretty darn close.  Here is how my exact ratio computations compared to Simplicity’s size chart:

Scaled 91%       Simplicity
Waist                23.66                24
Hips                 32.76                33

My experiment worked!

On paper.

Stay tuned for Part 2…

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23 responses to “Pattern Sizing Experiment: Part 1 – Grading vs. Ratios

  1. Mary Kay Reynolds July 10, 2013 at 1:34 am

    Brooke you are amazing; a seamstress and math wizard all in one. (I will need my engineer husband to help me with the math on this one 🙂

  2. sweary sewer July 10, 2013 at 2:26 am

    this is really, really interesting, thank you for writing.

    i have just graded up a 50s weskit pattern i had and the muslin suggests i managed to do it quite well. *gasp*

    with your method, i guess i have to have access to a photocopier, eh?

    looking forward to part 2. 🙂

    • Brooke July 10, 2013 at 3:45 pm

      Glad you liked reading about it! I’m not surprised you successfully graded your pattern – you’re better at the sewing thing than you think! =)

      And yes, you’d need a printer that can make copies to enlarge/reduce by a percent. I just copy on my inkjet printer and tape the pages together.

  3. Costume People July 10, 2013 at 10:21 am

    Thanks for this fantastic post. I admire your research!
    -Deb

  4. Karen July 10, 2013 at 8:18 pm

    Fascinating! And you are so right about the vanity sizing – I really don’t pay attention to the “number” anymore, just the bust measurement and the neck to waist measurement. (RTW is really bad with that vanity sizing!!)

    • Brooke July 10, 2013 at 10:00 pm

      I’ve learned to find my size on the rack based on how big something looks on the hanger. It’s amazing how many things end up on clearance racks just because a size label is numbered a little larger than normal!

      When it comes to sewing patterns, I usually go by the finished garment measurement chart (or measure the actual pattern if no chart included).

  5. Lorinda July 10, 2013 at 11:22 pm

    This is very interesting. I am looking forward to seeing how this works, and wondering if you are finding this works easily for many body types or just one very specific body type. I am also curioius to know if there might also need to be additional height (lengthen/shorten) adjustments too when you work with the ratio system. It could certain be a time saver even if it required a trip to a print shop.

    • Brooke July 11, 2013 at 7:30 am

      So far, it has worked well for me when dealing with enlarging kids’ patterns. The height lengthening and shortening is probably about the same as any pattern that you are fitting. For example, if a person is longer/shorter-waisted than the standard used, reducing or enlarging is not going to change the proportional relationship of the details and it will still need some altering. That is why I always make a mockup – makes stuff like that easier to fix. =)

  6. Gjeometry July 11, 2013 at 1:59 am

    Oooh, how exciting for 2 reasons. One, I have several patterns that are way too big for me that I’m dying to grade down. Two, I love math! On to part 2……

  7. Theresa in MéridaT July 13, 2013 at 7:49 am

    Wow, I don’t check your blog for awhile and you produce this great post! What size are patterns drafted in? What size is the prototype? It would make sense to buy that size if possible then use the photocopy method. This will be super for when I make stuff for the granddaughters!

    regards.
    Theresa

    • Brooke July 13, 2013 at 9:01 am

      Thanks! And glad you dropped by again! =)

      Most vintage patterns only come one size per envelope. I have a box of them in various sizes. The example in this post is one I have two copies of in two sizes – bust 34″ and bust 31″. I’ve used my shrinking and enlarging ratio method for different patterns in different sizes and it always seems to work well.

      I’ve mostly used it on modern patterns when it comes to girls’ dresses because I’ve sewn for a few girls who were tall and just generally larger than the size range offered in a pattern. Proportionally they were still girls, but they were big for their age.

      You can see the rest of my experiment with mockup examples in Part 2. =)

  8. Chuleenan August 15, 2013 at 7:37 pm

    I finally got around to looking up this post! Thanks so much for telling me about it. Grading up via a copier sounds like a pretty cool idea to me. 😉

    BTW – I ordered 4 patterns from VintageMartini.com. They should be coming any day now!

    • Brooke August 15, 2013 at 8:28 pm

      Glad you like the idea of using my ratio method! I would love to know how it works for you!

      Vintage patterns – exciting! Can’t wait to see which ones you bought. =)

  9. Martin Partlan (@martinpartlan) August 18, 2013 at 1:12 pm

    I am impressed that you grade manually. I use CAD software and still find it difficult because when I grade a new size inevitably there are discrepancies comparing the graded result to my table of measurements (I use PGM dress form measurements). It takes a bit of tweaking to fix the grading.

    • Brooke August 18, 2013 at 6:46 pm

      Oh, I only do the grading if I absolutely have to! That’s why I started trying to use ratios and a copier. I think every method involves some tweaking in the end unless you are drafting/draping from scratch for every person you sew for. And that’s why mockups will always be necessary. =)

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