How to check 1/4″ seam allowance: Pat Sloan’s simple trick

Raise your hand if it’s happened to you: you’re happily sewing along, creating a pile of pretty patchwork blocks. They look perfect—until you press and compare them. One block is too big, another is too small, and the rest are somewhere in between. How did this happen?!?

Best-selling author Pat Sloan will tell you: it might be your cutting. It might be your pressing. But most likely, it’s your ¼" seam allowance.

Even small inaccuracies can result in block-fitting hassles, row-sewing stress, and even sashing and border woes. So if you want to know how to fix a consistently too-wide or too-narrow ¼" seam allowance, read on for Pat’s sage advice!


Fixing an Inaccurate Seam Allowance
Excerpted from Pat Sloan’s Teach Me to Make My First Quilt

Sewing a consistent ¼"-wide seam allowance is very important in quiltmaking. Quilt blocks are generally building blocks of specific-sized squares, rectangles, and sometimes other shapes that fit together like a puzzle to create the final block in a specific size. And like a puzzle, if a piece is the wrong size, it won’t fit in its spot.

If your seam allowance is less than ¼", your units (or blocks) will be too big and your seam intersections won’t match. If your seam allowance is greater than ¼", your units (or blocks) will be too small, and once again, your seam intersections won’t match up and the final block will be the wrong size.

Even if you use a ¼" foot on your machine, you need to be sure you’re sewing an accurate ¼" seam allowance. Here’s an easy test to see if your seam allowance is accurate.

Place a small ruler (one with markings in ¼" increments) under the needle on your sewing machine. Slowly lower the needle by turning the flywheel by hand, until it barely touches the ruler. Adjust the ruler until the needle is on the ¼" line on the ruler and the edge of the ruler is ¼" to the right of the needle. Where is the ruler in relation to the seam guideline on your machine? Is it spot on? If not, you need to make some adjustments.

If your seam allowance is too wide, raise the needle slightly. Using the needle-position button on your machine, move the needle one position to the right. Carefully lower the needle and align it with the ¼" line on the ruler. If needed, repeat to move the needle one more position to the right.

If your seam allowance is too narrow, raise the needle slightly. Using the needle-position button on your machine, move the needle one position to the left. Carefully lower the needle and align it with the ¼" line on the ruler. If needed, repeat to move the needle one more position to the left.

Sometimes you simply can’t adjust the needle to match the seam guideline on the machine, because either you’re unable to move the needle to the correct position or your machine doesn’t have a needle-position button. In that case, place a piece of painter’s tape on the machine along the right  side of the ruler to make your own seam guideline that you can follow.

Recheck your seam allowance whenever you sew on a new machine, or if your blocks are not coming out the right size. Sometimes our minds wander and we’re no longer following the seam guideline.


Pat’s got tons of tricks just like this one in her “Teach Me” series of books—she’s taught thousands of quilters how to get better at their craft. Want to learn more with Pat too? Pick up one of her helpful books today:

Pat Sloan's Teach Me to Make My First Quilt Pat Sloan's Teach Me to Machine Quilt Pat Sloan's Teach Me to Sew Triangles Pat Sloan's Teach Me to Applique

Have you mastered a ¼" seam allowance?

  • Yep—and I re-check mine from time to time just like Pat.
  • It’s kind of hit or miss right now, but I’m going to try Pat’s tip!
  • Mastery seems like a looong way off for me . . . but I keep working at it.

Tell us in the comments!


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