Seam Allowance
Seam allowance is the extra width of textile added outside the pattern’s finished line, used for sewing pieces together and finishing edges.
Contents6 sections
Definition and Role
Seam allowance is the extra area added outside the finished line on a pattern (the reference line that becomes the product shape after sewing). It is necessary to join the cut textile pieces, and after sewing it becomes the area inside the seam or the edge finishing area.
The width of the seam allowance is set based on the design, the thickness and stretch of the textile, the sewing method, how easily it frays, and the sewing equipment used. It is important not only to decide the width itself, but also to give instructions so that everyone involved can handle it by the same standard.
Position in Product Making
In general product making, seam allowance is set during pattern creation after the design and specifications have been reviewed. After that, the process moves on to grading, marking, spreading, cutting, and sewing, so seam allowance design affects the accuracy of later processes, workability, and fabric consumption.
On the pattern, the finished line and the cutting line are distinguished, and notches, cut marks, and grain direction are added as needed. In the sewing workplace, pieces are joined based on the cutting line and notches, so if the seam allowance setting and notation are unclear, it can cause dimensional defects and left-right differences.
- The shape before adding seam allowance is checked based on the finished line.
- The cutting line is the outer line formed by adding seam allowance to the finished line.
- Sections with different seam allowance widths are clearly stated in both the pattern and the specification sheet.
Practical Setting and Workflow
Seam allowance is decided for each area to be sewn by checking the required strength, ease of sewing, seam thickness, and edge finishing method. Areas with strong curves, corners, or openings may be difficult to handle with a uniform width, so the shape must be considered.
In prototyping, the garment is sewn with the set seam allowance, and the appearance on the right side, seam strength, thickness, fraying, and discomfort when worn are checked. If revisions are made, the pattern, specification sheet, and cutting instructions are synchronized so that old versions are not left on the production floor.
- For thin textiles or textiles that fray easily, confirm the required amount including edge finishing.
- For thick textiles or areas with many layers, confirm the thickness when the seam allowances overlap.
- For knits or stretch textiles, confirm seam stretch and seam allowance waviness.
- For patterned textiles, confirm the relationship between the extra amount needed for pattern matching and the seam allowance.
Points to Note in Purchasing and Quality Control
Fabric order quantities are calculated based on the pattern cutting line. Changes to seam allowance affect fabric consumption and marking efficiency, so when changes are made, the required quantity of textile must be checked again. In particular, when there are restrictions such as fabric width, pattern direction, nap, or grain direction, it is necessary to consider extra allowance.
In quality control, check for insufficient seam allowance, variation in width, incorrect notch positions, twisting of the seam allowance, and seam allowance being caught in the seam. Even if the finished dimensions are correct, if the seam allowance is not handled properly, it can lead to fraying after washing, seam opening, and surface fading.
Differences from Similar Terms
A pattern refers to the overall template that shows the shape and reference lines of each part that makes up a product. Seam allowance is the extra area provided on that pattern, so it does not mean the same thing. A specification sheet is an instruction document for sharing seam allowance width, sewing method, finishing method, and similar details.
Grain direction is the standard for positioning parts relative to the lengthwise and crosswise directions of the textile, and bias means using the textile direction diagonally. These are design conditions related to cutting and stretch, and seam allowance has a different role as the extra amount needed for joining pieces together.
Frequently Asked Questions
Do all seam allowances need to be the same width?
No, they do not all need to be the same width. They are set according to the shape of the area to be sewn, edge finishing, thickness, strength, and sewing equipment. However, if the width differs by section, clearly state the width and handling method in both the pattern and the specification sheet so there is no confusion during cutting and sewing.
Does changing the seam allowance affect fabric order quantity?
It may. Widening the seam allowance increases the cutting area of the parts, which can change marking efficiency and the required fabric consumption. The effect is especially large when pattern matching, directional textiles, or narrow fabric widths are involved, so after the change, recalculate fabric consumption with the revised pattern before confirming the order quantity.
What problems are likely to occur if the seam allowance is insufficient?
It becomes harder to hold the textile during sewing, and seam opening, fraying, seam allowance being caught, and dimensional variation are more likely to occur. There is also not enough room for edge finishing and pressing, so it is important to confirm during the prototyping stage whether the necessary work allowance for the sewing specifications is secured.
