Some sewing patterns include seam allowance and others require you to add it. Check the exact pattern’s instructions and format before cutting. A publisher’s general convention is useful context, but an individual edge or pattern can have a different instruction.
Seam allowance is the distance between the cut edge and the intended seam line. If it is already included, adding it again changes the piece. If it is excluded, treating the printed seam line as the cut edge removes the material intended for the seam.
Publisher conventions are a starting point
| Source and format | Stated convention | Check before cutting |
|---|---|---|
| Tilly and the Buttons patterns | Its guidance describes included 15 mm/5/8 in allowances | The individual pattern’s allowance and any special edge instructions |
| Burda downloadable patterns described in its guide | Most do not include seam allowance | The file’s instructions, cutting layout, seam and hem requirements |
| A pattern in another format or from another publisher | No assumption follows from the rows above | The exact edition and its instructions |
Tilly’s guide to marking seam lines explains its stated allowance and marking tools. Burda’s downloadable-pattern guide describes its downloadable format, while the Burda FAQ addresses allowance and print-scale checks. “Most” is not “all,” and a downloadable-pattern rule should not be applied automatically to every envelope or magazine pattern.
The metric and imperial values in Tilly’s convention are sewing instructions in their respective units. They are not an exact mathematical conversion: 5/8 inch equals 15.875 mm. Use the unit and seam-guide setting specified for your pattern consistently.
Cut edge and seam line: a small calculation
Imagine a rectangular piece that is 100 mm wide from cut edge to cut edge. Its two side seam lines are each 15 mm inside the corresponding cut edge.
100 mm − 15 mm − 15 mm = 70 mm between the side seam lines
This is illustrative geometry, not a garment-fit calculation or a sewing test. Other seams, curves, ease and construction instructions can affect a real project. Its purpose is to show why included allowance and finished dimensions are different quantities.
Record seam and hem separately
A hem instruction need not match the seam allowance. Before cutting, make a short pattern record:
| Detail | What to record |
|---|---|
| Pattern and format | Name, version and whether it is a download, envelope or other format |
| Seam allowance | Included or excluded, stated width and exceptions |
| Hem allowance | Its own inclusion status and measurement |
| Print scale | The stated test-square dimensions and whether the print matches |
| Special edges | Any separate instruction for that piece or edge |
For a download, verify the printed test square against the pattern’s specified dimensions before evaluating or adding allowance. Correct allowance cannot compensate for a pattern printed at the wrong scale.
When choosing a project, the beginner sewing-pattern guide provides adjacent selection context. Confirm allowance in the actual pattern you select rather than carrying a convention across projects.
Method and limits
We compared the two pattern makers’ published guidance, checked October 11, 2026, and supplied a simple geometry example. We did not sew these patterns or establish a universal seam width. When the general guide and the actual pattern seem to disagree, resolve the exact file and instructions before cutting fabric.