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Stretch Factor - How to work out a fabrics stretch percentage

In patterns created for knit fabrics you will often see a note about the recommended ‘stretch percentage’ of the fabric. Put simply, stretch percentage is a measure of the fabrics ‘stretchy-ness’ and is the difference between your new pants fitting like a glove or you squirming around on the bed unable to get then past your knees. If you are new to knits, however, you may be tempted to gloss over this bit and wing it.

Now, I consider myself somewhat of an expert when it comes to shortcuts, work arounds and generally identifying the things I can get away without doing, but take it from someone who has created some seriously ugly and ill-fitting monstrosities over the years, stretch percentage is important!

Fortunately, stretch percentage is both super easy, and quick to measure. Here is how you do it:

  1. Grab your fabric and give it a little fold crosswise (that is selvedge to selvedge) and then take a 10cm portion of the fold between your fingers.

How to calculate stretch percentage

  1. Give it a stretch and measure how long the 10cm portion stretches to (this piece stretches to 14cm).
  1. To calculate the stretch percentage you take the length of your fabric when stretched, less the original length, divide it by the original length, and then multiply by 100.

In this example that looks like this:

(14-10)/10 x 100 = 40


There is a reason I said to grab a 10cm length, and it makes the whole thing a lot less complicated.

Grab your 10cm piece and give it a stretch. If it stretches an extra 4cm (so to 14cm in total) then it has a stretch percentage of 40%. If it stretches an extra 8cm (18cm in total), then it has a stretch percentage of 80%.

Get your stretch percentage right and the garment will fit like it should. Use a fabric with a lower stretch percentage and the garment will be a little snug or you will need to size up. Use a fabric with a higher stretch percentage and the garment will be baggier or you will need to size down.

And it is as easy as that.

A quick note on recovery (the other end of the equation)

Recovery is how well your fabric bounces back after you have stretched it, and is more a measure of the quality of the fabric than anything else. I try to go for fabrics with good recovery because after the effort of making something, it can be demoralising if my top gets wider or my trouser knees baggier as the day goes on, am I right?


As always, thanks for reading, if you have a go at sewing up one of our patterns, I would love to see, so be sure to grab some pics and hashtag them #threadfaction

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