How to Sew a Quarter-Inch Seam
Accurate 1/4" Seams are an Essential Secret of Successful Piecing
Jun 26, 2008
Do your quilt blocks keep turning out too small? Do the points of your stars or setting triangles get chopped off at the tips? Do the seams on your quilt tops not line up with each other? What’s going wrong? If your pieced blocks and tops don’t always turn out the right size and shape, the first thing to check is your seam allowances.
What is a Quarter-Inch Seam?
The seam allowance is the distance between your line of stitching and the raw edge of the fabric you’re sewing. One-quarter inch is the standard seam allowance used in almost every quilting pattern.
Why a Scant Quarter-Inch Seam?
Experienced quilters often advise beginners to try for a "scant" quarter-inch seam—a seam allowance that's just a thread or two less than a quarter-inch. That couple of threads matters because quilt blocks shrink slightly every time you press a seam open after sewing, when the top layer of fabric is folded over to one side. To compensate for this slight shrinkage and make sewn blocks come out exactly the right size, you’ll need to use a seam allowance of just a hair under a quarter-inch.
If your seams measure exactly a quarter-inch from the stitches to the edge of the fabric, your blocks will come out just a tiny bit too small. The more seams in your blocks, the more shrinkage you'll experience. This can cause real problems when you assemble a bunch of blocks into a quilt top. Leaving a scant seam allowance is most important when you make complicated patterns with lots of seams.
How to Achieve Perfect Scant ¼” Seams
- Use a quarter-inch quilting foot. Most sewing machines today offer a special foot with a built-in guide that helps you sew an exact quarter-inch seam. You may find that even with a special-purpose foot, it also helps to have a seam guide on your sewing machine bed.
- Create a seam guide on your sewing machine.This technique can help even if you’re already sewing with a quarter-inch foot. To create a guide, you will need a way to mark your sewing machine bed. The ideal seam guide is thick enough to make a little lip that keeps your fabric in place as you feed it into the machine. Some options other quilters use:
- Marker line drawn on the machine bed
- Stack of blue painter’s tape
- Thick foam tape like a Dr. Scholl’s foam bandage
- Piece of flexible cardboard
- Stack of Post-it notes
- A commercially available sewing guide that you can buy at a quilt shop.
- Put a rotary cutting ruler under the sewing machine’s presser foot and lower the needle until it touches a spot just a hair to the right of the quarter-inch mark closest to the right edge of the ruler. (You can also use a piece of graph paper and touch the needle to the first quarter-inch mark on the right side of the paper.)
- Using the right edge of the ruler or graph paper to align your tape or sewing guide, stick the guide on the machine bed just in front of the feed dogs.
- Run your fabric along the edge of the guide when you feed pieces under the sewing machine needle.
Test Seam Allowances for Accuracy
No matter what method you use to align your seam, you should check yourself with the quarter inch test.
- Cut three short, 1 ½”-wide strips of fabric.
- Sew the three strips together.
- Press the seams open, then measure the center strip. It should measure EXACTLY 1”. If it is narrower or wider, adjust your seam guide and retest, then check again.
Don’t worry if you don’t get your seam perfect the first time. You will get better with practice!
Learn more about successful quilting:
Choosing a size for your quilt
Choosing a sewing machine needle
How to prewash quilting fabric
