What Is a Seam Allowance?
Sewing an accurate seam allowance is essential in making a project work. If your seams aren't accurate, you may run out of fabric or the pieces may not line up correctly. So how do you make sure you maintain the proper seam allowance throughout your project? There are several ways:
Many machines have guide markers for you to align your fabric against to get a 1/4" seam. If your needle is set in the center position, keeping your fabric aligned with the guide marker will let you sew in a straight line and will result in accurate seam allowances. Check your manual to determine your machine's standard position.
Some machines come with a 1/4" presser foot or you can purchase one to fit your machine. If you line fabric edges up with the right-hand edge of a presser foot, it will push your fabric though the machine with a 1/4" seam allowance.
If your machine doesn't have a guide marker or 1/4" presser foot, you can still achieve the perfect seam allowance by creating your own guide. Measure 1/4" to the right of your machine needle. Mark that spot with a piece of masking tape. Push an index card through the machine along your tape guide. Because the distance between the lines on an index card is 1/4", your stitching should be on top of a printed line. If it isn't, adjust your tape guide and test the seam allowance with the index card again. Once you have the guide marker where you want it, add layers of masking tape to the first piece (we use five) to ensure the guide marker won't move.