Elastic length calculator

How the elastic length calculator works

Elastic only grips when it is shorter than the body part it goes around, so it has to be cut a little smaller than your measurement. How much smaller depends on the elastic. Wide, firm elastic stretches less and presses harder, so it is cut closer to the body measurement. Narrow, soft elastic stretches a long way and is gentle, so it is cut shorter. This calculator uses a rule of 10 to 15 percent less than the body measurement as a starting point. It is a common rule of thumb, not a standard, so always try the elastic on before you sew the ends. Here are the steps, in order:

Elastic around = body measurement × (1 − reduction)Cut length = elastic around + overlapReduction = 10 percent (firm and wide), 12 percent (standard) or 15 percent (soft and narrow)

Worked example. A 30 in waist with standard ½ to ¾ in elastic: 30 × (1 − 0.12) = about 26⅜ in to the nearest ⅛. Add a 1 in overlap and cut the elastic at 27⅜ in (69.6 cm). With firm, wide elastic the same waist gives 27 + 1 = 28 in, and with soft, narrow elastic it gives 25½ + 1 = 26½ in.

How to test it. Cut the elastic at the number above, pin the ends together with the overlap, and put it around your body or the cuff. It should feel snug, not tight, and not roll or dig in. If it is too loose, take a ½ in slice off the overlap and try again. If you cut it too short, you cannot add length, so start at the loose end of the range when you are unsure. For the pattern steps that thread the elastic through a casing, see how to sew an elastic waistband.

The most important check is that the opening still fits over the widest part. A pull-on skirt or pants has to pass over your hips, a cuff over your hand and an ankle opening over your heel, so the stretched elastic must reach that measurement. If it cannot, make the casing and the fabric piece wider rather than shortening the elastic less.

Elastic length chart

Lengths are rounded to the nearest ⅛ in. A pattern that states an elastic length always wins over this chart.

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Related guides

• How to sew an elastic waistband without twisting it
• What size sewing pattern do I need?
• Seam allowance explained: ¼, ⅜, ½ and ⅝ inch
• Elastic-waist skirt pattern