This post presents how to modify seam allowances.
Modified seam allowances are used in high-end designing departments and throughout the industry.


Marking patterns with varying seam allowances ensures faster, more accurate sewing, saves fabric, time, and effort, giving more professional results.  Cathy, Contemporary Fashion Education student demonstrates by modeling a blouse she made using these procedures. Cutting and sewing on the traditional 5/8 inch seam allowance, then trimming the seams after sewing means cutting the garment twice.

 In the diagrams below are some suggested seam allowances:

At the end of this post is a list of preferred seam allowances used in industry

If one traces the patterns as the seams are modified then the original printed pattern is left intact and can be easily referenced. Tracing paper, available at any art supply store, works really well. I buy the 50 yard 36 inch wide yellow canary. White is too opaque.

Tape the pattern to the work surface. Lay a sheet of tracing paper over the pattern. Tape the tracing paper to the work surface. Then trace the straight and cross-grain from the underlying pattern to ensure the tracing paper can be easily put back in place over the printed pattern if that should need to be done later.
Use a transparent ruler to mark the modified seam allowances. marking very short sections of the cutting line.
To reduce 5/8 inch seam allowances:
For a 1/4 inch seam allowance, remove 3/8 inch.
For a 3/8 inch seam allowance, remove 1/4 inch.
For a 1/2 inch seam allowance, remove 1/8 inch.
To increase 5/8 inch seam allowances:
For a 3/4 inch seam allowance, add 1/8 inch.

Curved seams that have stress, such as princess seams MUST have a seam allowance of 3/8 inch. Curved seams that do NOT have stress such as collars are usually given a seam allowance of 1/4 inch, but if the fabric frays easily use a 3/8 inch seam allowance.
Collars are given a 1/4 inch seam allowance on all seams.

Waistbands are usually given a 3/8 inch seam allowance on the waistband at the waist  A waistband must always have at least a 3/8 inch seam allowance at the waist as a 1/4 inch seam allowance is not strong enough to support the skirt. Other seams in the waistband usually are given a 1/4 inch seam allowance, but may have a 3/8 inch seam allowance.

SEAM ALLOWANCES used in the industry
 1/8 inch  Placket set’s lapel edge in knits. 
1/4 inch  Used in curved and/or difficult areas with no stress such as collars, neck, sleeveless armholes, cuffs, lapels and center front openings. 
3/8 inch   Used in curved and/or difficult areas with stress such as armholes with sleeves, sleeve caps, cuffs at the sleeve edge when finishing by sewing in the crack, waistbands at the waist, crotch curves, side seams in knits, some silky fabrics, invisible zipper sets in knits, and garments sewn on overlocks/overedgers. Some manufactured men’s suits have a 3/8 inch seam allowance on all seams. The industry uses a 3/8 inch seam allowance on fake fur, which is sewn on a mock-safety stitch. 
1/2 inch  Shoulder and side seams. Armholes that will be finished with serging. 
5/8 inch  Occasionally used in seams and zipper seams.  
3/4 inch  Zipper seams. Better garments’ side seams to allow for possible alterations. 
1 inch  Hems in budget and moderately priced garments. 
2 inches  Hems in better women’s garments. 
2 1/2 inches  Hems in better men’s pants. 
Seams that sew to each other almost always have the same seam allowance.

More later,

Laurel– published books


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