How do I lengthen or shorten a pattern?

Use the lengthen/shorten lines printed on the pattern, and do not simply add to or cut off the hem.

Why not the hem. A garment is shaped. Adding 5 cm at the hem of a flared skirt adds width as well as length, because the side seams are angled — the piece gets wider than intended. Removing at the hem does the reverse. On a bodice, adding at the hem moves the waist, which is exactly what you did not want.

The method. Cut the pattern piece straight across at the marked line. To lengthen, spread the two halves apart by the amount needed and tape a strip of paper in the gap. To shorten, overlap them by the amount needed and tape.

Then true the side seams. After spreading or overlapping, the side seam has a step in it. Redraw it as a smooth line through the adjustment — a curved ruler helps.

Do the same on every piece that seam joins. If you lengthen the front bodice, lengthen the back by the same amount, or the side seams will not match.

Where to adjust. Above the waist for a long or short torso; between waist and hip for skirt length; and above the elbow for sleeves rather than at the cuff.

Check the length on a toile rather than calculating it.