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How to Sew a Perfect 1/4″ Seam for Quilting

Psst! Don’t tell the Quilt Police, but sometimes I’ve had trouble making my blocks come out the right size. How about you?

Do any of these sound familiar?

  • Your quilt blocks end up a bit too small.
  • The points of your stars or triangles get chopped off at the tips.
  • The seams on your quilt tops don’t line up perfectly with each other.

What’s going wrong?

If your quilt blocks and tops don’t always turn out the right size and shape, one of the first things to check is your seam allowances. Seams that are just a whisker larger or smaller than a scant quarter inch can cause you a lot of trouble. (I know this from experience.)

If you can learn to sew a consistent quarter-inch seam, your quilt blocks will turn out the right size every time, and your rows will fit together perfectly when you assemble the blocks into a quilt. After years of giving lip service to the concept of perfect quilter’s seams, I decided to test my accuracy and walk my talk today.
Perfect quarter-inch seam

Definitions, Please

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. 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.

Why Do You Need a SCANT Quarter-Inch Seam?

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. This happens because when you press a seam after sewing, the top layer of fabric is folded over to one side. This makes the block shrink slightly. 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.

To compensate for the shrinkage and make sewn blocks come out exactly the right size, you’ll need to use a seam allowance that is just a hair under a quarter-inch.

How to Achieve Consistent Seams

Here are some suggestions for making your seam allowances come out the same size every time. No matter which method you use, you should still test your results to make sure you aren’t off by a hair in one direction or another. (More on that below.)

  1. 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. Not all machines have them. My fancy but finicky Pfaff 2140 has a quarter-inch foot accessory, but the Brother 1500s I now use for almost all my piecing doesn’t have one. So it’s option 2 for me!
  2. Create a seam guide on your sewing machine. I find this technique helpful even when I’m sewing with a quarter-inch foot. I can run the guide well out in front of the needle to help me align the fabric as I sew along. 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 I’ve seen here and there around the web:
    • Marker line drawn on the machine bed
    • Stack of blue painter’s tape. This is what I use. I stick several strips on top of each other to create a bit of an edge to align my fabric. Here’s the blue tape guide on my sewing machine.
    • Thick foam tape like a Dr. Scholl’s foam bandage
    • Piece of flexible cardboard taped to the machine bed
    • Stack of Post-it notes
    • Thick rubber band fitted around the sewing machine’s free arm (if your sewing machine has a free arm.) Thanks to blog reader Sue Hamner for this suggestion.
    • A commercially available sewing guide that you can buy at quilt shops or fabric stores. Dritz makes a magnetic seam guide which is supposed to work on any machine. I’ve also seen an adhesive seam guide from Collins that comes with a little measuring device for pinpoint accuracy.

How to Locate Your Seam Guide Accurately

Accuracy is the word here, so you’ll need to do a bit of measuring.

  1.  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.)
  2. 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. You don’t want the guide to interfere with those dogs!
  3. Run your fabric along the edge of the guide when you feed pieces under the sewing machine needle.

How to Test Quilt Seam Allowances for Accuracy

No matter what method you use to align your seam, you should check yourself with this quarter inch test.

  1. Cut three short, 1½”-wide strips of fabric like this: 
  2. Sew the three strips together.
  3. Press the seams to the sides, 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.
I decided to test the painter’s tape seam guide I was using on my sewing machine. I sewed the three strips together, pressed them, and measured. On the first try, the center strip measured less than 1 inch. It was TOO SMALL.
I moved the tape a bit closer to the sewing needle and tried again. This time, the center strip was TOO BIG. I had moved the seam guide too close to the needle.
On try #3, I got the center strip JUST RIGHT. Now my seams and my blocks should come out the right size.
The test didn’t take long at all — about ten minutes total. Why did I wait so long to do this?

Readers, I challenge you to try this test yourself and let me know how it turns out.

 Learn More About Quilting Basics

My best-selling book for new quilters covers quarter-inch seams and everything else you need to know to make your first quilts — and fall in love with quilting. Click on the image to buy it now. This link is an affiliate link, which means I earn a small commission if you buy anything through the link. Thanks for your support!

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{ 23 comments… add one }
  • Lynn Dedousis January 2, 2014, 7:05 am

    new quilter needs lots of help

    • Felicity Walker January 2, 2014, 8:43 am

      Lynn, if you have any questions, send us an email or post a comment and we’ll be happy to help as best we can. Glad to welcome you to the world of quilting. It’s a wonderful world and a (possibly) all-consuming creative interest.

  • APRIL January 16, 2016, 8:18 pm

    I STRONGLY advise against using the magnetic guide. I used the magnetic guide on two of my machines and it caused major problems with the metal bobbin shuttle jumping while I was sewing. To remedy this I had to stop using it for at least a week for all of the magnetic field to wear off before the machine would run normally again.

    • Felicity Walker January 16, 2016, 8:40 pm

      Thanks for that advice, April. I haven’t tried a magnetic guide myself. I have a fancy one on my new sewing machine, and before that I always stuck with a few layers of my trusty blue painter’s tape.

  • Carol January 18, 2016, 5:01 am

    No seriously, it really, really can’t be this simple… I almost feel like you are tricking ME!!! I am a FOURTH generation professional sewer, I gave dozens of aunties, cousins & nannys, and I have sewed for 40, yes, yes, 40 years, and I find this tiny little trick that has changed my life!
    You deserve a Nobel Prize of some description, yes you do. I love you by the way, I think I’ll keep an image of you in locket close to my heart!

    • Felicity Walker January 18, 2016, 7:37 am

      Aw, we’re blushing! So glad to have been helpful to you, Carol. I can’t tell you how much I wrestled with the perfect 1/4″ seam. I’m not one of those quilters who has an inborn gift for accuracy. But you can learn to be accurate even if you don’t have the gift already.

  • Jackie Anderson June 29, 2016, 2:43 am

    Very useful tip

  • Caroline July 8, 2016, 6:17 am

    Hi Felicity
    I had a lot of problems with my electronic machine not sewing properly and each time I took it to be tested it ran perfect and turned out that my magnetic pin holder that I had beside my machine was causing all the problems so after getting rid of it my machine now runs perfectly

    • Felicity Walker July 8, 2016, 7:32 am

      Oh, Caroline! Problems like that are so very frustrating. I am really glad you found the solution. Readers, be aware that anything magnetic such as Caroline’s pinholder or lights that attach to your sewing machine with magnets or magnetic seam guides can cause problems for electronic sewing machines. I guess that’s an argument in favor of sewing with an old-style mechanical machine.

  • Sue Hamner August 16, 2016, 4:29 pm

    I marked the quarter inch seam, then put a rubber band over the marking to give the lip. Works!!

    • Felicity Walker August 17, 2016, 10:59 am

      Great idea, Sue!

    • Brenda November 10, 2016, 4:44 am

      I love this idea, because it’s easy to slide the band over out of the way when sewing other projects. Like seams down the middle of my 1/2 blocks. Just had trouble finding the perfect rubber band, had to fit pretty tight, and be thick. My granddaughter’s make perfect seams!

  • Polly November 21, 2016, 2:03 pm

    I use a strip of moleskin to make an edge at the 1/4 mark. I never heard about using the scant 1/4 in. Thanks for the advice, my pieces should fit better knowing that.

    • cdmwriter November 21, 2016, 5:30 pm

      Great idea, Polly! Moleskin has the thickness that really helps guide the fabric. I might steal some from my husband’s hiking emergency kit and give it a try.

  • Dolores December 28, 2016, 1:05 am

    I must try this, now to make perfect Block

  • Erin January 10, 2017, 10:08 am

    Thanks so much for sharing. The quilts I made in the past were not even, you could see the gruesome results. The trick that is working for me are the note pads. It’s GREAT! Can’t wait to start a quilt. 😊

    • Felicity Walker January 10, 2017, 11:42 am

      Glad to have helped, Erin.

  • Nancy Stevens January 22, 2017, 7:34 pm

    I am thrilled to learn of this simple trick! Thank you so very much!

    • Felicity Walker January 22, 2017, 7:43 pm

      It’s our pleasure to give you useful information about quilting.

  • Kim January 27, 2017, 2:03 pm

    I am about to start my first quilt. It is going to be a joint venture between my mother and I with me (in California) doing the blocks and her (in Ohio) finishing it. Last night we were on the phone for an hour and she mentioned more times than I can count how important it was to make sure my seams stay at a perfect 1/4″. I’m sure this tip will help me greatly!
    Thank you!

    • cdmwriter January 27, 2017, 3:01 pm

      Best of luck to you and your mom, Kim! The quilts you make together will be double treasures because you both worked on them.

  • Cindy February 14, 2017, 1:08 pm

    Thankyou, Thankyou, Thankyou!!! My best friend is a professional quilter and she kindly set my 1946 Featherweight up with a seam guide, as you suggest… works like a charm!! I have to share my AH HA moment when I realized that the table runner my daughter and I were working on, on her new machine came out all wonky because we used the seam guide on her new machine and not one that was measured and affixed to her machine like mine… DUH!!! I am a remedial quilter, but open to become a real quilter😉❤

    • Felicity Walker February 14, 2017, 2:09 pm

      It sounds to us like you are well on your way, Cindy. You’ve already learned that there’s no substitute for measuring when it comes to accurate piecing. That took us YEARS to figure out.

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