Facebook Email Pinterest Twitter Instagram YouTube Icon Headphones Icon Favorite Navigation Search Icon Forum Search Icon Main Search Icon Close Icon Video Play Icon Indicator Arrow Icon Close Icon Hamburger/Search Icon Plus Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon

Top Down, Center Out Crotch Seam Adjustments

Threads #218, Summer 2022

Editor’s note: Pants-fitting instructor Ruth Collins offers an introduction to her innovate method in Threads #218, Summer 2022, in “Practical Pants Fitting” The approach she teaches helps most sewers fit most pants patterns successfully.

However, we’re all unique in shape and size, and there are inevitably some patterns whose grading or design present more challenges. If you’ve followed the steps outlined in Ruth’s article but haven’t achieved the exact fit you’re looking for, you may need to alter the crotch seam and inseams slightly. Read on to find out how to do that, working with the pants toile (test garment) you created for the initial fitting.

Go smaller or bigger

For this alteration, you’ll be using the overall pattern size you determined through the basic Top Down, Center Out process, but blending to a different crotch seam size. The easiest way to understand this is to look at a multisized pattern. The illustrations show the pattern’s cutting lines, not the seamlines, but the seamlines have the same relative size and shape.

Crotch Seam Adjustments: a typical multisize pattern
A multisized pattern includes the crotch seam for a range of sizes.

The back pattern shows how the crotch seam changes through the range of sizes. It is higher and shorter for the smallest size, and lower and longer for the largest size. If your initial fitting suggests you need slightly more or less body space to comfortably shape the pants through the crotch seam, you may want to try making the seam smaller or larger.

You will be working with your toile, which obviously doesn’t have the multisized lines on it. However, you can achieve the effect of making the crotch seam smaller or larger by sewing with a wider or narrower seam allowance. Go bigger by taking a larger seam allowance in the crotch seam and a smaller seam allowance in the inseam. Go smaller by taking a smaller seam allowance in the crotch seam and a bigger seam allowance in the inseam.

Crotch seam adjustments: adjusted stitching lines for different sizes


This altered seam allowance starts at the crotch point and blends up to the straight portion of the crotch line. For the inseam, start at the crotch point and blend the adjust seam allowance to just above the hem. For either option, do not exceed 5/8 inch.

If you need any changes to the back or front inseam at the crotch, blend the change to around the inseam’s thigh notch. Don’t extend this alteration more than halfway down the leg.

Refit the waist level

Keep in mind that any changes to the crotch inseams affect the crotch position. You need to start over matching up the waistband with the pants from the Top Down, Center Out, including any changes you may have made to the darts. When we created the toile, we provided sufficient allowance in the adjustment zone for this purpose. However, if you need a little more room for adjustment at the top, add a strip of fabric. In this process you are distributing the ease in a collaborative process between the pattern and your body.

Fitting yourself, by yourself, is an iterative process. You might not get perfect results on the very first go, but you can make additional refinements until you achieve the look and feel you prefer.

Illustrations: Ruth Collins and Steven Fleck.

Sign up for the Threads eletter

Get the latest including tips, techniques and special offers straight to your inbox.

Sign Up

Threads Insider

Get instant access to hundreds of videos, tutorials, projects, and more.

Start Your Free Trial

Already an Insider? Log in

Subscribe to Threads today

Save up to 42% and get a free gift


Log in or create an account to post a comment.

More From Threads

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |

Threads Insider Exclusives

View All
View All


Shop the Store

View All
View More