Seam allowance is the strip of fabric between the stitching line and the cutting line. It seems trivial, yet inconsistent allowance is a frequent cause of garments that will not assemble cleanly. Treating it as an intentional decision, set per seam, is a hallmark of careful pattern work.
This article covers common standards, when to deviate from them, and how seam allowance is handled in CAD when you export to DXF AAMA, PLT or PDF.
Common seam allowance standards
There is no single universal value, but conventions cluster. Industrial garment production often uses about 1 cm on most seams. Home and dressmaking patterns frequently use 1.5 cm. Hems, facings and zips usually carry more so there is fabric to turn and finish.
What matters most is that every edge meant to join its neighbor uses a compatible allowance, and that you record the value you used so it is unambiguous later.
When to vary the allowance
- Wider allowance on straight seams that may need future alteration, such as side seams.
- Narrow allowance on tight curves like a neckline, where wide allowance must be clipped heavily.
- Generous hem allowance for the desired fold depth plus finishing.
- Reduced allowance where seams cross, to limit bulk.
Net patterns versus cut patterns
A net pattern is drafted to the finished stitching line with no allowance. A cut pattern includes allowance up to the cutting line. Blocks are net; production patterns are usually cut. Confusing the two leads to garments that come out a size too small or too large by the total allowance.
Before cutting any new file, confirm which convention it uses. Made-to-measure files from Minerva Patterns state the seam allowance convention explicitly so there is no ambiguity at the cutting table.
Adding allowance in CAD
- 1.Finalize the net pattern with true-ed seam lines and matched seam lengths.
- 2.Apply seam allowance per edge, assigning different widths where required.
- 3.Generate corner treatments so allowances meet cleanly at seam ends.
- 4.Verify notches still sit on the stitching line, not the cutting line.
- 5.Export to DXF AAMA, PLT or PDF with the allowance baked in or flagged as a separate layer.
Pro tip
In DXF AAMA the stitching line and cutting line can be stored as separate entities, which keeps both the net and cut information intact for later editing.
Corner treatments and seam intersections
Where two allowances meet, the corner can be mitered, extended or squared depending on how the seam will be pressed. A correctly built corner means the allowance lies flat when the garment is turned and pressed, with no whisker of fabric poking out past the finished edge.
Pay particular attention to corners at hems and vents, where a poorly built corner shows on the outside of the finished garment.
Frequently asked questions
Is there a standard seam allowance I should always use?
No single standard applies everywhere. Industrial work often uses about 1 cm and dressmaking 1.5 cm, but you should vary it by seam type and always record the value you chose.
Why do some patterns have no seam allowance at all?
Those are net patterns or blocks, drafted to the stitching line. You add allowance yourself before cutting. This keeps the underlying shape clean for editing and grading.
Can I store both the stitching and cutting lines in one file?
Yes. The DXF AAMA format supports separate entities for seam lines and cut lines, so a single file can carry both the net and cut information.
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