How to use the elastic length calculator
- Choose inches or centimeters and enter the measurement around the body where the elastic will sit.
- Enter how much shorter the elastic should be than that measurement. The 10% shown is an example.
- Enter the overlap where the two ends join.
- Read the length to cut, and check how far the elastic has to stretch to reach the body.
Formula
joined length = body measurement x (1 - reduction)
cut length = joined length + overlap
stretch needed = body measurement / joined length - 1
A reduction of 10% means the finished loop is 90% of the body measurement, so the elastic stretches by about 11.1% to fit.
A 30 inch waist
For a 30 inch measurement, a 10% reduction and a 1 inch overlap, the joined loop is 27 inches and the elastic is cut at 28 inches. To reach 30 inches the elastic stretches 30 / 27 - 1 = 11.1%.
In centimeters, a 76 cm measurement with a 15% reduction and a 2.5 cm overlap gives a 64.6 cm loop, so cut 67.1 cm, which is 26.42 inches.
Choosing the reduction
How much shorter to cut depends on the elastic and on how snug you want the fit. A soft, stretchy elastic may need a larger reduction, while a firm one needs less. The 10% is only an example. Pin the elastic around the body, join the ends with a safety pin and test it before you sew.
Where the elastic goes also matters. A waistband that holds up heavy fabric needs a firmer fit than a cuff. Measure over the clothing it will sit on, not just the bare body.
Related sewing tools
Space buttons on the same garment with the Button Spacing Calculator, find the fabric you need with the Fabric Yardage Calculator, and size the edge finishing with the Bias Tape Calculator. For curtains, see the Curtain Fabric Calculator.
Assumptions and limits
- The elastic is joined into a loop with a flat overlap seam.
- The reduction is the share by which the finished loop is shorter than the body measurement.
- The page does not know how far your elastic stretches. Check the label or test a scrap.
- The body measurement is a single number. Take a fresh measurement if the fit matters.
Frequently asked questions
How long should I cut elastic for a waistband?
Measure around the waist, reduce it by the amount you want the elastic to stretch, and add the overlap. A 30 inch waist, 10% shorter with a 1 inch overlap, gives 28 inches.
How much shorter should elastic be than the waist?
It depends on the elastic and the fit. Many sewers try about 10% and adjust after testing. The page lets you enter any percentage.
Do I include the overlap?
Yes. The overlap is the part that is sewn flat where the ends join, so it is extra length you cut but lose from the loop.
How can I check that the elastic will stretch enough?
The page shows the stretch needed to reach the body measurement. Compare that with how far your elastic stretches without losing its shape.