• Prerequisites: Before you alter: reading a trouser, and when not to; Altering the waist: take in and let out.
• Time: 1–2 hours; longer with topstitching or a lining.
• Difficulty: moderate.
• Tools: seam ripper, chalk, long ruler, hip curve, pins, thread, overlocker or zigzag, iron and ham.
• Lined trousers: alter the lining by the same amount, but leave it 1/4 in (6 mm) looser so it does not pull.

1. Side insert: open the side seam from below the pocket to the knee or hem; set in a long narrow panel (a strip of matching or contrast cloth, or the trouser’s own hem allowance). On sportswear a contrast stripe looks deliberate.
2. Crotch gusset: for a tight inner thigh or crotch, open the inseams near the crotch and set in a diamond gusset. See Part V, Gussets and the crotch gusset.
3. Seat panel: rare, and visible; usually only for workwear or a much-loved trouser.
4. Find matching cloth: the hem allowance, the pocket facings, or a deep turn-up. Replace those with lining cloth.

An insert is honest work, not a failure. Show the wearer a sketch before you start.

• Pleated fronts: taking in at the side seams pulls pleats open; take a little out of each pleat depth instead, or keep the change behind the pocket.
• Side-seam pockets: take in above and below the pocket, leaving the opening untouched, or move the change to the inseam.
• Felled seams (jeans): see Altering stretch, knit and denim trousers.
• Trousers with a side stripe or piping: take in at the inseam only, or unpick the stripe and replace it.
• Left-handed: pin and mark with the trouser flat, working from the waist down on both legs, so you do not unconsciously take more from one side.

• Order: seat, then side seams, then inseams, then hem.
• Both legs: mark one, copy it to the other by laying them together flat, then check on the wearer.
• Taper: at least 6 in (15 cm) for a 1/2 in (1.2 cm) change.
• Grain check: after sewing, fold the leg along its crease. The side seam and inseam should lie evenly either side.

• Women with fuller hips and thighs: the size that fits the hip often needs only the waist changed; avoid taking in the hip “for shape”, which adds strain.
• Straighter figures: loose seat and thigh are common; centre back plus inseam usually solves it.
• Men with an athletic thigh: let out the inseam first; the side seam often has pockets in the way.
• Men with a flat seat: the classic fix is centre back plus a little back inseam.
• Children: do not take in seats and thighs to fit now; they need room to squat, climb and grow.

1. Share the change four ways to keep the leg straight.
2. Pin with the wearer sitting as well as standing; seats need room to sit.
3. Mark the crease with a line of tacking before you start, and check it after.
4. Taper long and smooth, never in a short step.
5. Use the old stitch line as a guide: measure the new line from it with a hem gauge every inch.
6. Sew from the hem up the inseam on both legs, so the grain is treated the same.
7. On a lined trouser, change the lining last, and slightly less.
8. Keep the cut strips: they become patches or gussets later.
9. For a crotch seam, sew twice, the second line just inside the first, for strength.
10. On wool, shrink away any fullness at the new seam with steam over a ham.
11. What professionals do differently: they look at the crease and grain after sewing, not just the fit.

The leg twists after taking in

1. Unpick and share the change more evenly between seams.
2. Re-press the crease along the true grain.
3. Prevention: never take a large change from one seam only.

The crease now runs off-centre

1. Remove the old crease with damp pressing and set a new one on the grain.
2. Move part of the change to the other seam.
3. Prevention: tack-mark the crease first.

The seat is now tight when sitting

1. Let out the centre-back seam on the curve by 1/4 in (6 mm).
2. Scoop the back crotch curve a little lower.
3. Prevention: sit-test before sewing.

Folds under the seat remain after taking in

1. Take in the back inseam near the crotch as well.
2. Check the rise; the fold may be length, not width. See Re-rise and crotch fixes.
3. Prevention: diagnose circumference, length or shape first.

The let-out seam splits

1. Resew a fraction inside, and back with a narrow strip of tape.
2. Add a small gusset at the strain point.
3. Prevention: leave at least 3/8 in (1 cm) of allowance after letting out.

Pocket bags pull or bunch after a side-seam change

1. Unpick the bag from the side seam and re-attach it on the new line.
2. Trim the bag to match.
3. Prevention: include the bag edge in the plan.

The lining pulls the trouser

1. Let the lining out by 1/4 in (6 mm).
2. Release a small pleat in the lining at the waist.
3. Prevention: alter the lining slightly less than the trouser.

• Myth: the side seam is where all width changes go. It is one of four.
• Mistake: taking in a seat until it fits standing, so it strains seated.
• Mistake: forgetting the other leg is a mirror, not a copy.
• Mistake: trimming the allowance before the second fitting.

1. Beginner: on an old pyjama, take in both inseams by 1/4 in (6 mm) from crotch to hem.
2. Improver: take in a trouser at the seat and back inseam for a flat seat; check standing and seated.
3. Confident: let out a tight thigh with a side insert, matching the grain and topstitching.

As a hobby: seat and thigh changes are how a “nearly” trouser becomes yours.

For earning: a straight leg after alteration is the mark of a professional; customers notice twisted legs at once.

For teaching: let learners take 1 in from one seam on one leg and share it four ways on the other, then compare.

• Finish every new edge before pressing open.
• Re-press the crease with a press cloth; see Part VI, Pressing as you sew, and setting creases.
• Wash cotton trousers once after a let-out to soften the old line.

• Do you share width changes between seams?
• Can you take in a flat seat?
• Do you check the crease and grain after sewing?
• Can you let out with an insert when there is no allowance?

Quiz

1. Why share a change four ways? Answer: to keep the grain and crease straight.
2. Where is a flat seat taken in? Answer: the centre-back seam, sometimes with the back inseam near the crotch.
3. How much allowance should remain after letting out? Answer: at least 3/8 in (1 cm).

• Flat seat: less seat curve than the pattern assumed, giving folds under the seat.
• Full seat: more seat curve than assumed, giving strain and pull lines.
• Insert: a strip of cloth set into a seam to add width.
• Asan: a common tailors’ word for the crotch or seat area; local use varies.

• Main source: D&D’s own trousers ebook, chapters 48–50 and 52 (distribute changes between side seam and inseam; flat-seat and full-seat changes), widened to men, children and inserts.
• Amounts and tapers are studio starting points. Teacher to check.
• Trade words (asan, golai) vary by region; studio to confirm.