How to Sew a Quilting Seam Allowance

  • 01 of 05

    It's Easy to Sew Quarter Inch Seams for Quilts

    How to Sew a Quilting Seam Allowance
    Get Set Up to Sew Quarter Inch Seams. Janet Wickell

    A quilting seam allowance is more narrow than the seam allowance used to make clothing.

    Quilters use a quarter inch seam allowance to create most quilt blocks and quilts. A few exceptions include paper pieced quilts, sewing a narrower or wider seam when you add binding to a quilt with borders, and the half inch seam allowances we use to make rag quilts.

    Why is it Important to Sew an Accurate Quarter Inch Seam?

    Sewing an accurate quilting seam allowance is essential. If seam allowances are off,...MORE patchwork pieces will not match-up with each other when it's time to sew components together.

    You might not notice a seam allowance that isn't quite right when you sew together batches of same-sized squares to make a quilt. If the seams are all the same width, patches will still align correctly. Incorrect spacing becomes a problem when sewing together patchwork units that have a different number of seams within their boundaries.

    Set Up the Sewing Machine to Test the Seam Allowance

    Let's set up the sewing machine to sew an exact quarter inch seam, the standard seam allowance used for quilts. Once you've mastered a quarter inch seam, your blocks will have units with sharp points and crisp corners, and they'll fit together perfectly when it's time to assemble the block or quilt.

    Some patterns recommend that you sew a 'scant' quarter inch seam allowance (see page 5). When you see the term used, make the seam allowance about a pencil line's width narrower than 1/4". You may find that a scant seam is best for all of your patchwork, so it's important to test your seam allowance before you begin to sew.

    Brush up on your rotary cutting skills and learn important pressing techniques before you begin.

    Materials Required to Test a Quilting Seam Allowance

    • Rotary cutting tools -- a cutter, mat, and long rotary ruler
    • Iron and ironing board
    • Sewing machine with a quarter-inch presser foot; use the standard foot if you do not have a quarter-inch foot
    • 2 light fabric strips, each 2" x 4"
    • 1 dark fabric strip, 2" x 4"
    • How To Cut Strips of Fabric for Quilts

    Have extra fabric nearby in case you need more test strips. 

    Continue to 2 of 5 below.
  • 02 of 05

    How to Test a Quarter Inch Seam Allowance

    How to Test a Quilting Seam Allowance
    Test Your Quilting Seam. Janet Wickell

    Test Your Seam Allowance

    1. Install a quarter-inch or standard presser foot on your sewing machine. If using a standard presser foot, try to determine which vertical groove on the machine's throat plate is equal to a 1/4" seam allowance.
    2. Align a 2" x 4" light strip with a 2" x 4" dark strip, right sides together and edges carefully matched.
    3. Sew the patches together lengthwise, feeding them through the machine with the 1/4" presser foot's right edge aligned exactly with...MORE the right edge of the patches. For a standard foot, align edges with the mark for 1/4".
    4. Sew another light strip to the opposite edge of the dark strip.
    5. Press to set the seams and then press seam allowances toward the dark strip.
    6. Use the rotary ruler to measure the dark center strip. It should be exactly 1-1/2" wide along its entire length. The outer strips should be exactly 1-3/4" wide along their entire lengths.

    If the dimensions of your pieced unit are accurate -- congratulations! You're ready to sew a quilt. If the size is a bit off, move on to the next page for more help.

    Continue to 3 of 5 below.
  • 03 of 05

    Tips for Sewing a Quilter's Quarter Inch Seam Allowance

    Check the Quilting Seam Allowance
    Check the Quilting Seam Allowance. Janet Wickell

    Inspect Strips Carefully

    • Were seam allowances pressed adequately? It's easy to "lose" width in patches that aren't fully pressed. Press again and recheck.
    • Make sure aligned strip edges didn't shift away from each other when you sewed the seam. If they did, try placing a very warm iron on top of the next set of strips before sewing to help them stick together, or secure the edges with fine straight pins before sewing. Remove the pins as the needle approaches.
    • Are the seams...MORE irregular, wide in some spots and narrow in others? Sew more slowly to improve accuracy. Set the machine to run at half speed if possible.

    Sew another set of strips, and then press and measure. If dimensions are still not accurate, don't worry, you'll get there with a few more changes.

    Consider Changing the Needle Position

    1. Cut additional 2" wide strips of fabric.
    2. Change the needle position if possible. Move the needle a notch to the right if you must shorten the seam allowance. Move it to the left if you must increase the allowance.
    3. Sew another test set, again aligning the fabric with the presser foot as described on page 2. Press and measure.
    4. If seams are still not accurate, place a seam guide on your sewing machine's throat plate as shown on the next page.
    Continue to 4 of 5 below.
  • 04 of 05

    How to Make a Seam Allowance Guide for a Sewing Machine

    Make a Quilting Seam Guide
    Make a Quilting Seam Guide. Janet Wickell

    Use a Seam Guide to Help You Sew

    Some sewing machines come with a seam allowance guide that can be positioned to the right of the needle, where it forms a ridge to butt the fabric against as you sew.

    Bernina's #57 patchwork foot has a guide built-in to its side.

    Rigid seam allowance guides are available commercially, but it's easy to make a guide from household materials.

    Make a Seam Allowance Guide:

    1. Place a rotary ruler under your needle, positioning its first 1/4" mark just below the...MORE needle's tip, with the rest of the ruler extended to the left. Check position by lowering the needle slowly by hand until it just touches the mark on the ruler.
    2. Make sure the ruler is positioned in a straight line on the machine by comparing placement with nearby grooves in the throat plate.
    3. Place a 1" piece of masking tape on the throat plate, its left edge flush with and aligned against the right edge of the ruler. Remove the ruler.
    4. Sew another test unit, guiding the right edge of your fabric along the left edge of the tape as you sew. Press and measure as before.
    5. If seams are accurate, stack additional pieces of masking tape on top of the first to build up a ridge for fabrics to butt against, or obtain height quickly by applying a piece of adhesive-backed moleskin on top of the tape.
    6. If your seams are still off, move the tape and try again. Continue tweaking and testing until seams are accurate.

    The feed dogs in some sewing machines are spaced widely enough to prevent the use of a seam guide -- it would cover them, but that type of sewing machine generally comes with a quarter-inch presser foot.

    Continue to 5 of 5 below.
  • 05 of 05

    Sew a Scant Quarter Inch Seam Allowance

    How to Sew a Scant Quilting Seam Allowance
    Sew a Scant Quilting Seam Allowance. Janet Wickell

    Scant Seams Are Often Best

    When you have adjusted your seam width to sew an accurate seam allowance, you may be sewing a 'scant' quarter-inch seam allowance, a seam that's a tiny bit less than the 1/4" wide.

    Rotary cut pieces are often slightly smaller than fabric cut with templates, due to the absence of marked lines. That narrow pencil line we used in the past to trace around templates wasn't very wide, but most of us tended to cut on the outside of it, adding a bit of excess. The width was...MORE often just enough to compensate for the loft that gets lost in a seam when it's pressed up and over the thread.

    Think of that missing line whenever you measure strips or sew seams. Accuracy takes practice, but it won't be long until you know exactly where to cut and where to sew to achieve the best results.