Are people shaped the same in the front and back? No, never.
Our bums are generally larger than our bellies (with the exception of maternity-wear), plus additional length is required in the back rise because we move our legs forward when we sit or walk, not backwards. So why is it that many pdf-format sewing patterns have mirrored Front/Backs? Sometimes the instructions say to cut the one pattern piece twice, for front and back. Sometimes a single pattern piece combines both front and back together by eliminating the side seam (often in pajama pants). In all my years of pattern-making from design school through private-label manufacturing through mass-market production, I’ve never seen a pattern drafted that way, ever. But in Indie pdf-land, it’s quite common. And it will never fit well.
What happens when pattern are mirrored front/back?
If the patternmaker started with the correct front rise and then used it for the back, there won’t be enough depth and length, resulting in “plumber’s crack” or “wedgies”.
If the patternmaker started with the correct back rise and then used it for the front, there will be excess fabric and puffiness in front when sitting down.
Why would anybody draft this way?
Some designers explain that the purpose is to print fewer pattern pieces. Others say it’s to eliminate mixing up the back with the front, or in children’s-wear it’s to let kids dress themselves. Problem is, it’s never going to fit as well as having a front and a back that are drafted separately to the correct shape. It’s a trade-off between “easier to sew” and “fits well”.
I reviewed this problem before but this time I’m going to show you how to correct it using the slash-and-spread method. Let’s say you’ve bought the cutest pattern design ever, but the drafting has mirrored rises in front and back, so you know already it won’t fit. You can fix this with a ruler, pencil, and measuring tape. For my example I’ll use “Daphne” by Violette Fields Threads. The charm of this design is in the ruffled knee-bands. The problem is in the rise (shape and length).
Here is Daphne in size 2. (It’s a single-pattern-piece design, but I cut it into 2 pieces down the side-seam so that you could see the rises together and visualize a human body fitting inside.) There is no indication anywhere on the pattern piece (or in the instructions) as to which side is the front and which is the back, and no notches, however one side is 1″ shorter than the other so I assume that’s the front (on the right, below). You can see there’s a SHAPE problem in both front and back….instead of a “U” shape that fits smoothly, there is a “V” that will cause “crotch bite” in front and “wedgies” in back:
Use a French curve to correct the rise SHAPE from a “V” to a “U”:
Now to correct the MEASUREMENT: the ratio between front and back rises should be about 2-to-3 , or 40% to 60%. In this case the front rise measures 6″ and the back measures 7″, which won’t cover the bum. Going back to high school algebra, use the ratio to calculate the new back rise measurement which is “X”:
Back rise/Front rise = 60%/40% = 3/2 = X/6″
3/2 = X/6″
Cross-multiply: 6″ x 3 = 18″
Divide by the reciprocal” 18″/2 = 9″
So the back rise should be about 9″. The way to achieve this is to “slash-and-spread” the back rise to extend the HEIGHT:
….and slash-and-spread the bottom of the back rise curve to add more DEPTH needed to fit under the bum:
Put the pattern pieces back together :
Now check against a well-fitting pattern (in this case Oliver and S “Sunny Day”) and you can see that the measurements are a lot better.
You can go back in and smooth the edges with a French curve:
Now compare your new “U” shape, which will fit around the front belly and up -and-over the bum, to your original “V” shape:
And now you have a well-fitting pant, that also has the adorable knickers cuff trendy detail! No more sacrificing fit for fashion.