Elastic Length Calculator

Elastic only holds a garment snugly if it is under tension when worn, so it has to be cut shorter than the body circumference it sits against and then stretched to fit. Relaxed Length is that shorter, at-rest length (Body Measurement times the Stretch Ratio), and Cut Elastic Length adds a small Overlap for Joining on top so you have fabric to stitch the loop closed.

No. Overlap for Joining only changes how much total fabric you cut -- it is added after the tension calculation is already done, purely to give you material to overlap and stitch the two ends together. Stretch Amount scales with Body Measurement, but Stretch Percentage and Comfort Rating depend on Stretch Ratio alone -- they measure how far the elastic stretches relative to its own relaxed length, which is the same 25% at an 80% ratio whether the waist is 24 inches or 44. Overlap for Joining affects none of the three.

75-85% is the typical working range for most garment elastic: waistbands generally sit toward the higher end (80-85%) for comfortable all-day wear, while tighter applications like wrist cuffs or leg openings on activewear may use a lower ratio (down toward 75%) for more hold. Lower Stretch Ratio values mean more stretch is required to reach the body measurement, which raises Stretch Percentage and can push Comfort Rating down if pushed too far. Note that the two rules of thumb diverge at the extremes -- the other common guidance is to cut elastic simply 1 to 2 inches shorter than the body measurement, which at a 44-inch waist is a much gentler reduction than 80% would give.

Comfort Rating is driven by Stretch Percentage, not by Stretch Ratio directly -- it measures how far the elastic is stretched relative to its own relaxed length, which works out to Stretch Ratio and nothing else -- neither Body Measurement nor Overlap for Joining moves it. A stretch ratio at the low end of the typical range can still push Stretch Percentage past the 25% comfort threshold this calculator uses, especially for elastics that are already narrow or firm, so treat the rating as a flag to test the elastic on your body before committing to a full cut.