Elastic length calculator
Enter the measurement where the elastic will sit and how firm the elastic is: you get the finished loop and the length to cut, overlap included, for waistbands, wrists, ankles or sleeves.
Waist, wrist, ankle or arm, measured snugly.
Percentage of the measurement: 90 to 95 % for most elastics.
To join the ends; 0 if you butt them on a patch.
2 for a pair of cuffs or legs.
Elastic to cut
Pin the loop and try it on before sewing it closed: elastics vary between brands, and comfort is personal.
Cut elastic a little shorter than the body measurement so it holds without digging in: loop = measurement × 0.90 to 0.95, then add about 2.5 cm (1 in) to overlap and join the ends. For a 72 cm waist and medium elastic, 72 × 0.92 = 66.2 cm for the loop, so you cut 68.7 cm. In inches, a 28 in waist gives a 25 3/4 in loop and a 26 3/4 in cut.
Which percentage for which elastic?
The firmer the elastic, the closer to your measurement you cut it; a soft, stretchy one is cut shorter to hold the same.
| The elastic feels | Cut at | Typical elastic |
|---|---|---|
| Firm: hard to stretch, snaps back | 95 % | Woven and non-roll waistband elastic |
| Medium | 92 % | Knitted elastic |
| Very stretchy and soft | 90 % | Braided elastic, lingerie and narrow elastics |
These are starting points: elastics vary a lot between brands. Before sewing the loop closed, pin it, put it around you where it will sit and adjust until it holds without pinching.
What should I measure?
- Elastic waist: measure where the waistband will sit, at the natural waist or lower. On pull-on garments only the elastic is cut to the waist: the casing and the garment are cut wide enough to pass over your hips.
- Cuffs and sleeve hems: measure around the wrist, ankle or arm where the elastic will sit, snugly. Allow a little more at the upper arm so it stays comfortable when you bend your elbow.
- Pairs: set the number of pieces to 2 for two cuffs or two legs, and the calculator gives the total to buy.
How do I join the ends of elastic?
The usual way is to overlap the ends by 2.5 cm (1 in) and stitch a box or a few rows of zigzag stitch through both layers. For less bulk, butt the two ends together over a small patch of fabric and zigzag across: then set the overlap to 0.
Thread the elastic through the casing with a safety pin, checking it has not twisted, before joining the ends. Then close the casing and spread the gathers evenly. Sewing an elastic waistband casing covers each step.
Sewly's patterns with an elastic waist, such as the pull-on trousers, list the elastic length in the notions, worked out from your waist.
Frequently asked questions
How much shorter than my waist should elastic be?
Usually 5 to 10 % shorter, so 90 to 95 % of your waist depending on how stretchy the elastic is. For a 72 cm waist that is 65 to 68 cm before the overlap; for a 28 in waist, 25 1/4 to 26 5/8 in.
Do I add seam allowance to elastic?
Add the overlap you use to join the ends: about 2.5 cm (1 in) when you overlap and zigzag. If you butt the ends together on a patch of fabric, add nothing.
Why did my elastic waistband get loose?
Elastic relaxes with wear and heat, and stitching through braided elastic weakens it. Open a few stitches of the casing, pull the elastic out, shorten it and close it again.
What width of elastic should I use?
2.5 to 4 cm (1 to 1 1/2 in) suits most adult waistbands, and Sewly's patterns use 3 cm by default. For cuffs and sleeves, 6 mm to 1 cm (1/4 to 3/8 in) is common. Make the casing slightly wider than the elastic so it slides through.