Pattern Modifier
Upload a pattern PDF, select a piece, and apply seam allowance, lengthen/shorten, or grading modifications. Download the modified pattern — all in your browser.
How it works
The tool reads your pattern PDF, analyzes the vector drawing commands, and identifies large closed shapes as pattern pieces. You select a piece, choose a modification, and the tool applies the change to the actual geometry — producing a new PDF with the modified piece.
The output includes both the original outline (dashed gray) and the modified outline (solid blue) so you can verify the change visually. A 1" test square is included for scale verification.
Three operations
Seam allowance
Add or remove a uniform seam allowance around the entire piece. Standard amounts: ¼" (quilting), ⅜" (indie), ½" (Closet Core), ⅝" (Big 4). Useful for Burda patterns (no SA included) or when converting between standards.
Lengthen / Shorten
Add or remove length at a horizontal slash line. Specify the amount and where to slash (as a percentage from the bottom of the piece). The tool splits the piece and offsets one half.
Grade
Scale the piece up or down by a percentage in width and/or length. This is uniform scaling — professional grading varies the amount at different points, so use this as a starting point and adjust critical seam points manually.
Confidence levels
Each modification reports a confidence level:
- High — geometric operation is well-defined and applied precisely (e.g., uniform SA offset)
- Medium — operation applied with assumptions (e.g., slash position is estimated, grading is uniform)
- Low — piece detection was uncertain, verify the result carefully
Always verify the modified piece against your original before cutting fabric. The dashed overlay shows the original outline for comparison.
Limitations
This tool works best with vector PDF patterns from digital pattern companies (Illustrator, Affinity, Inkscape). It parses the actual drawing commands to find piece outlines. Scanned patterns, raster images, or heavily complex PDFs may not detect pieces correctly.
For tiled (multi-page) PDFs, use the Tiled → Plotter converter first to assemble the pages into a single large page, then upload the assembled PDF here.
Your PDF never leaves your browser — all processing is client-side.