Confident beginner · 4–5 hours · 9 steps
How to sew a elastic-waist trousers
Elastic-waist trousers are the most-worn thing most people ever sew. There is no fly, no waistband fitting and no zip, so almost all the work is in two seams and a casing — but the crotch curve is where the comfort comes from, so it pays to understand it.
How it's constructed
- Silhouette
- Wide or tapered leg, full length or cropped
- Shaping
- Front and back crotch curves; back curve is deeper
- Waist
- Folded casing with flat elastic, or drawstring
- Pockets
- In-seam or slanted front pockets
- Hem
- Double-turned hem or wide cuff
Fabrics that work
- Linen and linen blends for summer
- Tencel or viscose twill for drape
- Cotton flannel or corduroy for winter
What you'll need
- 25–40 mm flat elastic
- Safety pin or bodkin for threading
- Pocket lining fabric if you use slanted pockets
The steps, in order
- 01
Choose your size by hip, not waist
With an elastic waist, the hip measurement decides whether the trousers fit. The waist adjusts itself.
- 02
Cut two fronts and two backs
Note that the back pieces are wider and have a deeper curve. Mark them straight away so you do not mix them up.
- 03
Add the pockets
For in-seam pockets, attach the pocket bags to the side seam allowances before joining the side seams. For slanted pockets, sew and understitch the pocket opening now while the pieces are flat.
- 04
Sew the inseams
Join each front to its back along the inside leg seam. Finish the allowances and press.
- 05
Sew the side seams
Join the outer leg seams, catching the pocket bags where relevant. Press.
- 06
Join the two legs at the crotch
Turn one leg right side out and slide it inside the other, matching the crotch curve. Stitch the whole curve in one pass and stitch it a second time for strength — this seam takes the most stress.
- 07
Make the elastic casing
Fold the waist edge down twice, slightly wider than your elastic, and stitch close to the fold — leaving a 5 cm gap at the centre back.
- 08
Thread and close the elastic
Thread the elastic through with a safety pin, try the trousers on to check the tension, overlap the ends by 2 cm and stitch them securely. Close the gap and add a couple of vertical stitch lines through the casing so the elastic cannot twist.
- 09
Hem to your own length
Try the trousers on with the shoes you will wear, mark the length, then turn the hem up twice and stitch.
Mistakes worth avoiding
Sewing the crotch seam before the leg seams
Do the inseams and side seams first. Reversing the order makes the crotch curve almost impossible to feed through the machine smoothly.
Pulling the elastic too tight
Fit the elastic to your waist relaxed, not stretched. Too tight and the casing rolls over during the day.
Forgetting to secure the casing
Without vertical stitches through the casing, the elastic twists in the wash and never sits flat again.
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