How to Size Up a Sewing Pattern

Follow the slash method to enlarge your favorite patterns.
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Pattern-making enthusiasts can follow specific steps to enlarge or reduce existing patterns, referred to as grading. Most pre-made patterns include grading lines for sizes ranging from extra small to extra large for knits, or sizes 2 through 16 for woven fabrics. Enlarge patterns using the slash method, also referred to as cut-and-spread. This process splits existing patterns at specific points to add width to desired areas of the pattern such as the waist or side seam. Take body measurements with a flexible tape measure prior to revising a pattern.

Things You'll Need

  • Straight Pins
  • Scissors
  • Pattern Paper
  • Drafting Pencils
  • Tracing Paper (Optional)
  • Tissue Paper
  • Removable Tape
  • Graph Ruler

Spread the existing pattern on a work table. For instance, to enlarge a pattern for a sleeveless top, open the front and back bodice sections separately. The dart details on a pattern piece generally appear as diamond- or triangle- shaped inserts, which will contour the garment when stitched closed. Most patterns indicate the darts with a broken line.

Trace the existing pattern onto pattern paper with drafting pencils. Keep the original intact for future use. Transfer all data to the traced copy, including cutting instructions and seam allowances.

Draw a line from the bodice hem to the dart’s pivot point with a clear graph ruler. The pivot point refers to the dart's point of intersection. For example, a shoulder dart generally looks like an upside down vertical triangle insert. The point is referred to as the pivot point.

Cut the line from the hem to the pivot point with scissors. Avoid cutting through the pivot point. This process is referred to as the slash method. This step enlarges a fitted bodice by adding width to the waistline and increases the distance from side seam to side seam.

Pin the dart with straight pins and spread the slash according to the desired width. For instance, if you are adding 2 inches to the bodice waistline, spread the slash line 1 inch for the front pattern and 1 inch for the back pattern. If you slash the front and back 2 inches, the finished pattern adds 4 inches to the overall bodice, resulting in a loose fit.

Place a piece of tissue or tracing paper underneath the slash opening.

Tape the top pattern to the bottom insert to hold the slash line in place with removable tape.

Remove the straight pins from the dart and retrace the enlarged pattern onto another sheet of pattern paper. Copy all cutting instructions, grain lines and seam allowances to avoid cutting mishaps with the revised pattern.