In order to sew pieces of fabric, you must include excess fabric at the edge, called a seam allowance. This seam allowance goes beyond the stitching line. When sewing, the needle penetrates the fabric on the stitching line with the garment to the left and the seam allowance to the right.

Home sewing patterns typically use 5/8” / 16mm seam allowance. No one knows for sure why this value was adopted. Some people believe it reduces errors by using the same seam allowance on all patterns and all seams. It also appears that 5/8” / 16mm is a balance between a too wide and too narrow seam allowance. Patternmaker Pro gives you full control over your seam allowances.

A seam allowance varies in width depending on the seam finish, the fabric, where the seam is placed and the type of sewing machine used.

Most fashion manufacturers use 1/2” / 12mm for average seams on garments.

Seam allowance of 1/4” / 6mm is used at enclosed seams or very curvey seams such as necklines and facings. You might want to allow a wider seam allowance of 3/4” / 19mm when sewing in zippers.

When you are fitting basic block garments, a very generous seam allowance of 1” / 2.5cm is preferred. This allows you lots of room for making adjustments and better fitting.

When sewing with a serger or overlock machine, you’ll want to take into account the cutting blade distance from the furthest left needle. To make a nice trim of any fraying edges, you’ll want the seam allowance to be outside the cutting blade. For example in imperial, if the distance between the needle and blade is 3/8”, you may choose to use a 1/2” seam allowance. This will trim 1/8” off the edge. In metric, if the distance between the needle and blade is 9mm, you may choose to use a 12mm seam allowance. This will trim 3mm off the edge.

Patternmaker Pro gives you the ability to adjust the seam allowance to fit your particular application. When you create each measurement set, you will designate your preference for Imperial or Metric. Seam allowances will be displayed based on this preference.

Seam Allowance Suggestions

1/4 Inch - 6mm

  • All faced areas
  • Sleeveless armholes
  • Narrow spacing
  • Extreme Curves

1/2 Inch - 12mm

  • Armholes with sleeves
  • Waistlines
  • Center Lines
  • Stylelines

Side Seams & Zipper Seams

1/2" to 1" - 12mm to 25mm


3/8 inch - 9mm