The technique commonly known as the scant seam allowance will forever change the piecing, precision, and final result of your quilting projects. A quilt is always more impressive when the seams of each piece land exactly where they should. When you spend countless hours on a project, you certainly want the final result to reflect your hard work.

The universal standard seam allowance for a quilt is ¼ inch. However, when you sew many pieces of fabric together to make a quilt and press the seam allowance to one side, the thickness created by ironing can slightly reduce the width of each piece. Even if this difference is as small as about 1 millimeter, when you add it up across all the pieces in a quilt, you can lose ¼ inch, ½ inch, 1 inch, or even more in overall width. That’s a significant difference for a project that relies on seam accuracy.

Instead of “cheating” your seam allowances by manually stretching them or pulling with the iron, the scant seam allowance technique — essentially adjusting your seam allowances — makes all the difference and can save you a lot of headaches.

In this video, Caroline explains how to perform the scant seam allowance test.

Note: The video is available in French only, but you can turn on YouTube subtitles (CC) to help follow along in English.

The principle is simple: before starting your quilt, you sew a small test strip using a few fabric pieces, then check whether your actual seam allowance matches the expected finished width.

Materials needed for the test:

• 5 or 6 fabric strips (or pieces) from your project
• a quilting ruler
• your sewing machine

Sew the 5 or 6 fabric pieces together with a ¼ inch seam allowance to create a fabric strip. 

Measure the total length of your sewn strip and compare it to the theoretical length you should have.
If there is a slight loss or a small excess, it means your ¼" seam allowance needs to be adjusted.

If you notice a loss in width, it means your seam allowance is slightly too wide.
Move your sewing machine needle just a tiny bit to the right to reduce the seam allowance.

Less common, but possible: if you have extra width, your seam allowance is slightly too narrow.
Move your sewing machine needle just a tiny bit to the left to increase the seam allowance.

Repeat steps 1 to 3 using your new needle position until you achieve the exact expected width.

You can now start sewing your quilt with peace of mind!

To avoid re-testing every time you pick up the same quilt project, make yourself a cardboard template with a stitch marking the exact position of your adjusted seam allowance.

• The more seams your blocks contain, the more noticeable the impact of an imperfect ¼" seam allowance will be. If you already see a loss with just 5–6 strips, imagine the effect on a queen-size quilt!
• The loss can appear horizontally, vertically, or even diagonally, depending on the pattern.
• Each cotton fabric has a different thickness, which is why it’s recommended to do this test before every project.
• If you’re mixing different fibers (for example cotton, minky, or linen), the test becomes even more important to avoid unpleasant surprises.

Now that you know this trick for successful piecing, you’re ready to create all the quilts of your dreams!

Happy quilting!