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Truing Pants Side Seams

AnneAudette | Posted in Fitting on

What’s the best way to plumb the side seam of pants?  I don’t understand what I need to do.  I haven’t been able to find any photos/sketches/instructions at the library or on the web.  I know I need a fitting partner.  Do I use a yard stick?  Plumb line?  A laser tool?  Does anyone have detailed instructions what to do with the current seam if it is not perpendicular to the floor?  My fitting partner knows less than I do.  Help!



  1. user-51823 | | #1

    don't know what technique the experts use, but here's what i'd do.
    make a muslin pair from an easy pattern you like. wearing them, have a friend mark the straight vertical using either a tall carpenter's level or a chalk snapline (also a carpenters' tool).
    remove and cut along your new mark, disregarding the original seam. draft your new pattern from this, adding seam alowances. make another muslin (or any cheap scrap fabric) from the new pattern before you try it out on moer expensive fabric. hope this helps-

    1. AnneAudette | | #2

      Thanks for your ideas.  I like the chalksnap idea.  I will buy this tool.  My hips are wide and flat; my legs are thin!  How do I position myself and the chalksnap tool?  Will one "snap" cover the entire side seam?  Will several "snaps" need to be done?

      Thanks again.


      1. user-51823 | | #3

        hold one end of the snap line at the side center of your waist and let the other end dangle close, but not touching, the floor. gravity will find a true vertical. then have your buddy hold bottom end tight to the floor against your foot, and snap at about mid-calf, then at thigh. that should do it but you can snap again anywhere you need to.

  2. Teaf5 | | #4

    The plumb of the side seam is determined by the way the pants fit onto the waistband, not by the cut of the side seam. If the pants are too long in the back, the side seam will sway forward; if too long in the front, it will sway backward.To check this out, make that trial pair of pants, including the zipper but do not attach the waistband. Cut the pieces out as per the pattern, but leave an extra couple inches all the way around the top. Put on the pants, and then slip a elastic belt or knotted elastic band on top, at your comfortable, normal waistline.Then look in the mirror, and tug up or down on different areas of the pants until the side seams hang straight (you can use a weighted string hanging from the elastic to check this). Keep adjusting until the pants hang well and look good in front and back, and then use chalk or marker to draw the waistline along the elastic band.Take off the pants and smooth them out on a flat surface, and then lay the pattern piece on top. You'll be able to see your personalized waistline seam clearly and can correct the one on the pattern. If one hip is higher than the other, you can mark left & right hip on the different lines.Since the waistlines on different patterns are fairly consistent and will probably fit you the same way, you can make this same adjustment on every pattern without have to go through the fitting process again.

    1. Josefly | | #5

      Teaf5 has given you correct info about the cause of un-plumb side seams - it's in the waist seamline. The pants-fitting pattern I'm using also says to make the trial pants without putting on the waistband, pinning the zipper opening closed, and tying elastic around the waist over the pants at the waistline, as Teaf5 suggested. Then pull up at the center back and down in center front if the side seams are swinging forward (a cause for this might be full tummy and/or flat derriere). Mark the new waistline just at the bottom of the elastic, and transfer the changes to your pattern.

      1. AnneAudette | | #6

        Thank you so much for the fitting ideas using the waist area to "true" the side seams.  It makes sense to me.

        Please keep the comments coming!


  3. From my Stash.... | | #7

    Hi. Teal5 is correct with her suggestion. I would add to her comment that in addition to adding inches at the waist band of your muslin, I would also add an inch to the side seam allowances so that if the side seam is pulled off-plumb below the waist/hip area, you still have extra material to "push and pull" those side seams straight. Examples for when you may have to do this:

    - extra weight on the inner thigh,

    - thicker calves,

    - knock-knees or bow-legs.

    Everything else Teal5 applies.

    Good luck with this.


    1. AnneAudette | | #8

      Thank you very much.



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