Guides / 02—08
Seam allowances and hems do different jobs
Joining two pieces differs from folding a visible outer edge. Plan each edge as part of the pattern.
Allowances belong to joins
A seam allowance provides space to stitch two edges. Its width depends on the pattern, fabric and finishing method; no single number suits every project. Mark the stitching line and how pieces meet. If a panel has a join on both sides, add space at both sides.
Hems belong to outer edges
A hem folds a fabric edge for a tidy finish and to control fraying. A double-fold hem needs material for both folds; it does not automatically equal the seam allowance. Decide each fold depth before sizing the cut piece, then test on a scrap to see how bulky it becomes.
List every edge
Draw a rectangle and label each edge: seam, hem or another treatment from the pattern. Add material only where required. If the finishing method changes, calculate the cut dimensions again.