Pants Fitting: Determine Your Crotch Curve with a Pants Fitting Muslin

Fitting pants can be challenging even for the most seasoned sewists among us. Given all our unique (and amazing!!) bodies, making a pants fitting muslin is a must. So good for you if you’ve done your due diligence and made a muslin. But how do you assess the needed changes and translate those to pattern adjustments? Below are some tips from fit expert Rae Cumbie.

Find the full article in the October/November 2018 issue of Sew News.

Working out your personal pants fit is so much easier if you begin with a mock-up that has horizontal and vertical lines drawn on to guide your adjustments. Women’s bodies come in an infinite number of shapes, and a basic pant mock-up will help you understand where your curves diverge from the “standard” size and adjust the pattern for future pants stitching success.

If you’re really serious about concurring your pants fitting-challenges, here’s how to get started. Choose a simple tapered pant pattern for non-stretch fabric. The essence of obtaining a good pants fit is to develop a pattern that reflects your unique crotch curve, then you can shape the pants pattern and style them for any type of fabric.

Getting Started with Your Pants Muslin

  • Use a light- to mediumweight non-stretch pants fabric to create a mock-up.
  • Choose your size based on your largest measurement. If you have an oval shape body, your waist/abdomen measurement might be larger than your hips.
  • Cut out the pattern and then your fabric. Transfer the grainline and the lines for horizontal adjustment (the crotch lines, lengthen/shorten lines or HBLs) onto the fabric right side using a permanent dark marker. Mark the darts too, but don’t sew them in.
  • Construct the basic pants seams using a long machine basting stitch so you can make adjustments easily. (Don’t sew darts, add waist or zipper.)
  • Put on the pants and anchor them at the waist using an elastic tie. Pull them up so the crotch curve is sitting in a comfortable place close to the body. Don’t worry if there’s lots of extra fabric above the elastic, or if the pants legs are too full. These issues will be addressed after the crotch is perfected.

Position the pants in an effort to get the grid of lines to sit parallel and perpendicular to the floor.

Reading Horizontal Balance Lines

Get a friend to read the grid of lines on the back first, observing the back crotch to assess for each of these issues:

  • If the horizontal lines dip at the center back, this means the crotch extension beyond the curve needs to be lengthened. Add the length where the inseam and crotch curve converge and ease the inseam back to its original line at the notch. Add the amount that the dip suggested you need.
    pants musling crotch extension
  • If the grain lines bow out, forming parenthesis around your bottom, or there’s excess fabric in the seat, then the crotch curve needs to be reshaped. Pinch out the excess fabric and pin the adjustment in place until the grain lines run parallel to each other and the pants sit smoothly across the seat.
  • If you’ve pulled a sizable amount of fabric out of the center back, shorten the crotch extension so the pants are pulled closer to the body. Changing the crotch curve on pants is a very counterintuitive exercise. If you scoop the center back to make the pants tighter, it actually lengthens the crotch extension.
    pants fitting muslin shorten crotch curve

You might have to make several changes, one at a time, to get the grid of lines straight. Be patient and move each successful change to the paper pattern so your next pair of pants will reflect your adjustments. Consider making a second sample to test your pattern changes if you’ve made lots of adjustments in your quest for an excellent crotch curve. Once the back curve is looking good, use the same techniques of observation and adjustment to clean up the front crotch curve.

Once the mock-up has the correct crotch curve, keep the grid of lines straight as you shape up the side seams, establish your preferred waist and drape in any necessary darts so the waist and hip area fits smoothly on your curves. Walk and sit in your adjusted pants to check the fit. Remember to transfer all these adjustments to the paper pattern, too.

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