How to Sew a Quarter Inch Seam Accurately

Posted by Elaine Huff on

Today I thought I'd share some tips for sewing an accurate quarter inch seam allowance when piecing your quilt blocks. There are several things that can affect your seam allowance and we'll go through a few of them.

Update: Toward the end of the post I added a tip from my friend Brenda about measuring 1/4" on your sewing machine bed.

seam allowance

Before Piecing:

First, I recommend pressing your fabric before cutting - especially if there are wrinkles in the fabric. You can also use a spray starch to make your fabric a bit more stable. Currently, I'm using Best Press but I've also made my own by buying the concentrate at the grocery store and mixing it with water in a spray bottle. Starching really helps if you are working with thinner fabric and/or you've prewashed your fabric.

Second, test your seam allowance. The easiest way I've found is to take three 2.5" squares and sew them together in a row, press the seam allowances and then measure the center square as shown below. The center square should measure 2" from seam to seam. If not, you need to adjust your seam allowance width.

accurate piecing

You can also test your seam allowance by sewing a four patch unit using 2.5" squares. In this case the four patch should measure 4.5" square. As you can see I'm off a little bit at the bottom!

seam allowance accuracy

There are several factors that affect piecing.

Fabric thickness:

When you press the seam allowance, you are folding the fabric at the seam allowance and that tiny fold takes up a bit of fabric. The thicker the fabric you are working with, the more that fold makes a difference.

Thread Thickness:

Also, thread thickness takes up a tiny bit of fabric. 40 weight thread is thicker than 50 weight and so will take up more space in the fold. 

When combined in a block with 6+ seam allowances, those tiny amounts can add up and either distort your block or make the finished size incorrect.

Scant Quarter Inch Seams:

A lot of quilters go by the rule of sewing a scant 1/4" seam when piecing. "Scant" means a couple of threads less than a true 1/4" seam. And it works well most of the time.

Tools that Help:

Use a quarter inch foot on your sewing machine. You'll still need to test it to make sure it's really accurate.

You may also need to adjust your needle position.

Use 50 weight thread because it takes up less space.

No quarter inch foot? You can measure 1/4" from your needle and put painter's tape on the bed of your sewing machine to mark where that is. Be careful not to cover up your feed dogs!

quarter inch seam

If you have a seam guide/rail for your machine (mostly older machines have this accessory), you can set that up for 1/4" seams.

seam allowance accuracy

newsletter signup

Brenda had this great tip for sewing a more accurate 1/4" seam. If your machine has the markings on the throat plate or bed, this may be a helpful tip for you.

"I have had trouble making a true 1/4" seam always. After reading and trying your tips, I still wasn't accurate enough.
"My machine has a 1/4" mark on it. I discovered that I had been moving the fabric until the mark was covered. Now I position the fabric so it touches the left of the line. What a difference!"
Thanks Brenda!

measuring 1/4" seam


Honestly, the best way to become more accurate is to keep piecing more blocks and quilts! Enjoy the journey. Don't worry about being "perfect", just piece to the best of your ability and know that you will improve.

I hope you've found this post helpful. If you liked this post and want to see more articles like this, simply click here to sign up for my newsletter and also receive a free PDF quilt pattern called Chained Weathervane.

Happy Quilting!


P.S. A few years ago, several friends and I made a bunch of Kim Diehl's Simple Whatnots quilts. While her quilts are awesome, they are small! Making all those little blocks really improved my piecing! She has put several of those patterns into two books. The one I especially like is the Simple Whatnots - A Batch of Satisfyingly Scrappy Little Quilts. Check it out if you are interested.

simple whatnots quilts 

P.P.S. To print a PDF of this tutorial, check out the free app at

Share this post

← Older Post Newer Post →