Adjusting Side Seams: The 3-Inch Rule

When it comes to sewing garments, the biggest challenge is getting the fit just right. Fit! Fit! Fit! The importance of achieving the right fit can’t be overstated.  It’s what turns a homemade garment into a professional looking one.

Red Garment with Overlaying Graphic Text Measurements
Photos via Simply Sewing Studio

One important fitting adjustment that affects all types of garment is the side seams.

Adjusting side seams can sometimes be a guessing game, especially when doing them on ourselves, but they don’t have to be. Implementing this simple 3-inch rule method makes the process an easy and effective way to fit ourselves as well as others.

Step 1:

Begin by pinning the side seams together, wrong side to wrong side, along the usual ⅝” seam lines. Make sure those pins run parallel and not perpendicular to the seam edge.

Step 2:

Now, try on the garment. With the garment on the body, adjust the pins to where they need to be for the fit you desire. In most cases, it’s the hip line and waist that need the most adjusting. It’s important adjustments are made on both sides of the garment and pinned all the way to the hemline. Do your best to pin as evenly as you can on both sides, but don’t worry, the 3-inch rule will ensure the final seam line is evenly balanced on both sides.

Step 3:

Remove the garment, making sure to leave all the pins along the side seams in place.

With tailor’s chalk or a fabric marking pen, mark a line perpendicular to the side seam line (within the seam allowance only), beginning at ⅝” down from the top edge, and then at 3″ increments, as illustrated in the photo below. Do this on both the right and left sides of the garment.

Depiction of Sewing Measurement Chart and Garment

Step 4:

Now take a piece of paper and make four columns. Down the side of the paper mark ⅝”, then 3″, 6″ and every 3″ increment thereafter for as long as your garment’s total length. At the top of the page title, the next column the LEFT SIDE (of the garment), the fourth column is the RIGHT SIDE. The middle column will become the new adjusted seam allowances so title it NEW AVERAGED SEAM ALLOWANCE.

In the Left Side column, write down the seam allowance distance from where the side seam pin is located at the ⅝” mark. Next record the distance at the 3″ increment, then the 6″ increment, etc. until you reach the hemline. Now, do the same to the other side and write those measurements into the Right Side column.

In the center column, enter the measurement that averages the left and right measurements. Using the 12″ increment as an example, on the left side the pin marking is 1″, while the right side is 1 ½”. This means the new seam allowance will be 1 ¼”, or the average of the 2 different measures. Once you have your averages calculated by each increment, you are ready to redraw your side seam lines.

Step 5:

Take out the pins from your fitting. Using the new averaged side seam allowances, make a mark along the side seam line, using a tailor’s chalk or a fabric marking pen, at each increment on the wrong side of the garment.

Using a Seam Gauge to Measure Seam

Step 6:

Using a hip curve ruler, draw the new seam line by connecting the markings on each side of the skirt. This new line forms the guideline to use to sew in the side seams. Repeat the process on the opposing side. Trim your seam allowances if necessary and finish the seam as usual. The 3-inch rule ensures both side seams are now even and balanced.

Marking Seam on Garment

To learn more about getting the perfect fit, including adjusting side seams and pattern alteration, check out Joi Mahone’s Fast-Track Fitting or Lynda Maynard’s Sew the Perfect Fit.

Come back to the Craftsy blog tomorrow for a tutorial on how to finish seams without a serger!

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2 Responses to “Adjusting Side Seams: The 3-Inch Rule”

    I am extremely grateful for this article. It has made the difference between sewing or just giving up!!!

    • Rosemary Barrett
      Rosemary Barrett

      Great information. In section 3 your written paper at the 6” middle column should be 7/8”