Perfect Quarter Inch Seam Allowance

Quilt Instructions for the Beginning Quilter

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The 1/4" seam allowance (it's not uncommon to see it abbreviated in quilt patterns as SA) is standard for all types of quilting.

It's big enough to hold the patches together and small enough to reduce bulk and save fabric.

Learning to sew an accurate 1/4" seam is the first step to enjoyable quilting.

Your blocks will fit together easily and finish up square. Quilting is a pleasure because they lay flat.

All because of an accurate seam allowance.

Seam Allowance - Shmeam Allowance!

Why is it so important?

When your 1/4" is off, your blocks will never be accurate.

Log Cabin block

This log cabin block has
10 seam lines top to bottom
and left to right

Example: The log cabin block to the right with 1" wide logs should be 11-1/2" before it is sewn into a quilt. It has 10 seams top to bottom and left to right.

If every seam stitched is off by a mere 1/16", your block would be off by...

10 seams X 1/16" = 5/8"

You block would measure either 10-7/8" if the seam allowance was too big or 12-1/8" if it was too small. That's a lot to be off for a block.

Now if each of those blocks is sewn to a pre-cut sashing strip that is 11-1/2" long, you can see where inaccurate seam allowances makes your efforts more of a pain than a joy.

Stitch as accurately as you can.

When a Quarter Inch Isn't 1/4"

When quilters refer to the 1/4" seam allowance they are really talking about a "scant" 1/4".

In quilting, the seam is stitched, then pressed closed to set the seam, and then opened and pressed with the seam generally towards the darker fabric.

A wee bit of the block fabric is "lost" in the "turn of the cloth" or where the fabric folds back on itself when the patches are opened.

With thicker fabrics (think flannel) more fabric is lost in this "turn of the cloth". Use a thicker or heavier thread for stitching seams and even more fabric is lost.

To make up for this loss, quilters set their machines for a "scant" quarter inch seam.

Now we have to find it!

Tools for Stitching a Good Scant Quarter Inch

There are several handy tools and gizmos available to help you sew a perfect 1/4" seam allowance.

Quarter Inch Foot

Quarter Inch Foot

The edge of this specialty foot is a quarter inch away from the needle. It is a good option for machines that can't make needle position adjustments.

There are several versions on the market. The "Little Foot" is a clear version of it.

Notice how the feed dogs are exposed on the right side. Some quilters believe they don't get enough traction with this foot because of it.

Edge Stitching Foot

Edge Stitching Foot

My personal favorite. This one looks like your standard presser foot but with a flange on the right side as you sit facing your machine. The raw edges of your patches ride along this flange as you stitch. Starch your fabric to make it even easier.

NOTE: You must be able to adjust your needle position to use it properly.

Make Your Own Seam Guide...

Use masking tape, moleskin or Post-It-Notes to create your personal quarter inch seam guide. Here's how.

make a seam guide with masking tape
Seam guide made with masking tape
  • Grab the same ruler you use to cut your patches.
  • Place it under the presser foot and hand lower your needle until it is touching the right side of quarter inch line. (Remember, we're looking for a "scant" 1/4".)
  • Making sure that your ruler is squared up with the lines of your sewing machine, lower the presser foot to hold the ruler in place.
  • Butt a piece of masking tape straight up against the ruler and position it in place.
  • Remove the ruler and complete a sewing test with the fabrics you'll use in your piecing. Adjust the masking tape as needed.

As long as your presser foot doesn't extend beyond this quarter inch line, either moleskin or a short stack of Post-It-Notes can be used instead of the tape. Either one will create a higher fence or guide.

For machines with a drop-in bobbin, this method may be more trouble than it's worth. You'll need to re-tape every time you replace your bobbin.

...Or Purchase One

Purchase from Keepsake Quilting

If you find you are having trouble getting your ruler lined up properly to apply the moleskin or tape above, you might want to try the Perkins Dry Goods' Perfect Seam Guide.

Simply put it under your presser foot, then lower your needle into the hole on the guide.

Lower your presser foot onto the guide to hold it in place. Add your tape or moleskin along the right side just as you did above. Presto!

Check Your Accuracy with a Sewing Test

Regardless of what you use for a seam guide, you'll need to do a simple "sewing test" to check for accuracy. It's easy to do.

Step 1

Cut three strips of fabric each 1-1/2" wide by about 4 inches.

Step 2

Sew two strips together along the 4" side.

Step 3

Sew the remaining strip to a 4" side.

Sew the strips together

The arrow points to the anchor cloth that I stitch onto before sewing any
seams. This prevents my machine from 'eating' the edge of the first piece.

Step 4

Press the sewn unit flat to set the seam.

Press flat to set the seams

Step 5

Now press the patch open, with all your seam allowances pressed towards the darker fabric.

Press the seam allowance towards the darker fabric

Step 6

Measure the finished block with your usual rotary ruler.

Measure the sewn strips


It should measure exactly 3-1/2" wide by about 4" long. The two outside sewn strips should measure exactly 1-1/4" wide, each, and the center strip should measure exactly 1".

If the strips are too wide, your seam allowance is too small, increase it.

If the strips are too narrow, your seam allowance is too big, reduce it.

It is crucial to having a happy and satisfying quilting experience that your seam allowance is accurate.

There is nothing more frustrating than finally having the time to work at your machine, only to find that your seam allowance was off and ALL of your stitching must be ripped out in order for things to fit together. ARGGGHHH!

One final point...

Your perfect quarter inch seam allowance will change for different fabric and thread combinations. Flannel is a thicker fabric. You may need to use an even "scanter" seam allowance.

The only way you'll know for certain is to do a quick test.

Do take the time to retest for each new  project. The few minutes you spend to test your seam allowance can save you hours of frustration from trying to piece patchwork that just won't go together.

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