How to Sew an Accurate Quarter Inch Seam

by Deborah

Sewing an accurate 1/4” seam allowance throughout your quilt construction is essential so that all pieces will fit together properly.

First, select a seam guide and then test it for accuracy. The guide lines on the throat plate are not always accurate, so do not trust these measurements without testing first. Even a slight deviation will multiply with the number of pieces sewn together to make a quilt top.

Choosing a Seam Guide

1/4” presser foot: Some machines come with this specialty foot, but if not one is usually available to purchase. Even with this foot it is still a good idea to test your seam allowance for accuracy, since these feet don’t always produce an exact 1/4” seam. Some machines allow you to move the needle position to the right or left if necessary to achieve that perfect 1/4” seam allowance.

Adhesive: You can make your own with blue painters tape or use a commercial adhesive guide such as Collins Machine Seam Gauge & Adhesive Guide.

To make your own, first lower the feed dogs so that the measuring devise will lay perfectly flat, position a piece of graph paper or a ruler on the bed of your machine and slowly lower your needle to the center of the 1/4” mark. Keeping your ruler straight, position the tape along the right edge of the ruler just ahead of the needle.

Remove the ruler and test your seam allowance for accuracy by running the right edge of your fabric up to the left edge of the seam guide. Realign if necessary. If using painters tape, build up a ridge with three to four layers of tape for the fabric to butt up against.

How to Test Seam Allowances for Accuracy

Cut three 1-1/2” x 4” strips of fabric. Sew the strips together lengthwise with a 1/4” seam allowance. Press the seam allowances towards the center strip. The center strip should now measure exactly 1”. If it does not you will need to adjust your guide and retest again. Be patient; it will pay off in the end!