For the longest time, I knew nothing about determining the stretch of a particular fabric, nor did I understand why it was so important. If I had a knit sewing pattern that I wanted to make and a knit fabric that I liked, I would combine the two and figure out the fit along the way. Knit fabrics are stretchy after all, right? There would be some wiggle room.
And for a long time this method of sewing worked for me. That is, until I got to my “problem” areas i.e. my thighs and calves. For the longest time, most of my garments were focused solely on my upper torso. I sewed primarily fit & flare dresses or things that were a bit looser in fit, so I never had to worry about, or even contemplate, that my lower half doesn't always fit within one standard size set.
Then one day I was trying on a pair of ponte knit leggings and I suddenly realized that stretch was SUPER important. My calves could barley breathe in these leggings, let alone attempt any sort of movement.
I love these leggings, but my calves are squeezed in there pretty tight.
So I set down a rabbit hole of learning how to determine stretch in a particular fabric and how to match that with a sewing patterns recommendations.
Luckily, most pattern will come with a stretch guide somewhere on the pattern. It might be on the back of the pattern packet, inside the pattern booklet, or on the pattern somewhere itself. When you have access to one of those stretch guides, use it!
If your pattern didn't come with a nifty stretch guide, it's really easy to determine the percentage of stretch for your fabric with nothing more than a ruler and your fabric in hand.
I like to do things the easy way, with the least amount of brain power involved (gotta save that for the actual sewing!). The easiest way to determine stretch, I have found, it to take a small segment of your fabric and fold it in half, either on the grain or cross grain. Don't worry too much which one you are measuring here as you will want to measure both to determine your fabric's Direction of Greatest Stretch (DOGS).
Line up your folded fabric with a ruler. I like to put the majority of my fabric near the 0” mark and then slide the cut end/ selvedge end over until it reaches 10”. At this point of the process, no stretching should be happening.
With one hand, you will want to hold down the fabric that is near the 0” mark so that it doesn't move.
With the other hand, take your cut edge/ selvedge edge near the 10” mark and tug on it.
There is a delicate art to this part where you are pulling your fabric to see how far it will stretch, but without pulling it SO far that it is being over stretched. With time, you will get the feel of this, but generally it's quite obvious when you have overstretched your fabric.
This is me, clearly overstretching the fabric. I am using all of my hand strength to pull this fabric a little too tightly.
My fabric stretched from 10” to 13”. That means that my fabric has 30% stretch going in this direction. How did I come up with that? Well, my fabric is able to be stretched by 3”, and the formula I use to determine stretch when working with 10” is (3/10) x 100 = 30%.
But the easiest way to remember is to look at the second half of the number (so for my 13” that would be 3), add a zero (30) and a % sign (30%)!
Once you have done one direction of your fabric (i.e. grain vs cross grain), you can go ahead and follow the same steps to check the stretch percentage of the other direction.
Once you have both percentages, you will be able to determine which of the two directions has the greatest amount of stretch, which is typically important (and noted!) in patterns and pattern piece placement.