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Trueing the Waist: Sansahash “Imari” Shorts

I’m always on the lookout for a good kids’ shorts or pants pattern. Compared to the sheer volume of children’s dress and skirt patterns, pants are few and far between. Well-fitting ones are even more elusive. The newly-released Sansahash “Imari” shorts pdf is a very cute style which comes in bubble and regular versions. The pattern prints out and fits together perfectly.  However, the center-back seam is not trued at the waist, which makes it difficult to stitch on the waistband, and a challenge to fit smoothly along the back waist. There’s an easy fix for this, which I’ll show you.


The center-back seam of elasticized-waist pants should be trued to a 90-degrees (right) angle.  Low-waisted jeans and hip-huggers can have a larger-than-90-degree (obtuse)angle, as they are shaped at center-back from (smaller) waist down to (larger) bum.  But basic sitting-at-the-waist, elasticized pants require a 90-degree right angle at center-back, otherwise the waist won’t lay flat: there will be a peaked pop-up at the center-back waist, that will form a bubble when the elastic is inserted.

Compare these two kids’ shorts center-back seams:

  • Left: Sansahash “Imari” with a 70-degree acute angle at the waist
  • Right: Oliver & S “Sunny Day”  with a 90-degree right angle at the waist


Post Script: a reader asked about Pattern Emporium “Honeybuns”; they also have a 90-degree angle a center-back waist:


I know from experience that “Sunny Day” fits well; let’s see what happens with fitting “Imari”. I cut out a muslin (this is a 12-month size for ease of photography); after stitching the backs left-to-right and attaching the back yokes (I changed the sequence-of-stitching to factory-method), this is the resulting shape:


I didn’t make a mistake here, this IS how it’s supposed to look as per the instructions:


Side note: the details look like jeans, however a classic jeans pattern will create the opposite shape (a “valley”, not a “peak”) before the waistband is attached.

You may wonder how this peak will fit when on the body.  Since the stress area on bottoms is (first) going horizontally around the largest part of the body (secondly it’s vertically going down under the rise/crotch), watch what happens:


The peak caused by the acute angle at the center-back makes the waist pop up, away from the body. The excess fabric can be pinched out, and the muslin actually creates it’s own  90-degree trued corner (which I marked with a pencil onto the muslin):


Side note: “Post-Its” are very useful for checking trued corners! Perfect little squares….

Let’s see what happens when the back is stitched to the front at side-seams and crotch, making a three-dimensional muslin:


Layed flat, you get the same peak, which becomes a pop-up, that can be pinched out:


On the dressform (I don’t have a pants form, so don’t look at the crotch fit, only the waist)…..peak, pop-up, pinch out:


Without making any alterations, I stitched on the waistband, to see how that would affect the shape. The waistband structure pushes the peak downwards, which creates a bubble:


On the dressform  you can see again how the waistband pushes the peak down into a “bubble”, and the excess needs to be pinched out.  The goal here is to make the waist measurement about the same as the full-hip measurement…the waist will then be pulled in with the back elastic:


PS: Keep in mind that the waistband size needs to be as big as the hip size, to get the shorts on, since the front fly is “fake”….however an excess at center-back which isn’t useful in getting the shorts on isn’t going to help, because there is no body fullness at the center-back-waist, above the bum. It’s a concave body area, not a convex one. 

Would putting in the waist elastic help the fit? Yes it does pull in the waist to fit against the body….however it still creates that bubble above the fullest part of the bum which needs to be pinched out:





The easy way to eliminate the “peak-that-turns-into-a-bubble” is to true the pattern’s center-back seam at the waist, using a 90-degrees right-angle :


(If you don’t have a ruler, then a Post-It or even the corner of any sheet of paper is fine.)

Then adjust the back yoke and back waist to correlate to the measure of the the back bottom upper edge:


Side note: I also French-curved the center-back seamline to make the shapes consistent throughout the size range, for future use:


I un-stitched the muslin, re-cut the center-backs/yokes/waistband, re-stitched (badly…see the ripples?!)….and voila! No more peaked angle, no bubble to pinch out:


The waistband is ready to easily insert the elastic:


(We’re leaving on vacation so I didn’t have time to make up the pattern in “real” fabric.)

So, if you find a pants or shorts pattern that you love, but the waist looks peaked and bubbly, it could be a simple matter of trueing the center-back seam to make it behave and lay down smoothly.

Happy Sewing!

Best, Janet



  • Saskia Bregazzi

    This is so useful!
    I have made trousers/shorts for my daughter and always wondered about the peaked centre back seam and why it was there. This explains that weird lumpy bit that I always get when using these patterns (note, not the ones you talk about in this post, but several other ones I own by totally different designers).
    It will definitely revisit these patterns now with a view to truing the back seam to make them sit flat.

  • [email protected]

    I imagine it might be there because the designer wants to make sure the waistband is as large as the hip, for ease in putting on the pants…..however it’s much better in that case to add fullness to the side-seam (as adult patterns do, to slip over the hip-bone) than the center-back.

  • fat_lady

    Well-written, fair, easy-to-understand explanation as usual, Janet. I also love how you always manage to find something positive in every pattern; it comes from your true depth of knowledge of pattern drafting.

    I really, *really* don’t understand why pattern ‘drafters’ do this, though. Do you? It has no logic (that I can see) from very basic knowledge of the geometry of the human body, or even from the experience of wrapping pieces of cloth around oneself as a child playing dress-up, which I suppose is a very elementary sort of draping.

    Are they all following the same set of faulty instructions from some dodgy ‘e-course’ with the blurb ‘You too can be a designer, pay $$$$ here!’, or do they not have the sense to interpret what their eyesight, be it even as poor as mine, must surely tell them? Or …?

  • [email protected]

    It’s a complete mystery to me why this happens so frequently! You find a pattern with great design concept, a style you’d really love to make, and then…..there’s just one weird fitting error that can be so easily tweaked. Yet somehow it was overlooked by everybody from the designer, to the grader, to the team of testers.

    Yes there are definitely cases of “the blind leading the blind”. The basic pants sloper in the (otherwise lovely) book from The Cottage Mama has mirrored front/back rises…and since it was in a hardbound book, I’ve heard that designers took it as gospel and copied it.

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