The most accurate answer would be that the gusset is the open space you see when you split your pants. In simple terms (unless you have been dancing really, really wildly and really, really split your pants) it would be about the length of the seam you open and about as wide apart as that the resulting opening would be.
A gusset is giving a particular garment what it needs anyway.
What is also interesting to me as someone who has sewn a number of different shaped gussets over the years is that the different shapes, most commonly a diamond about 3"+ long and about 2"+ at the widest part in the middle, and a V shape, all work in a similar way. But think about your own physiology and consider what shape you need and where.
What is common to them all is that one side is usually attached to a top of the leg seam (either to the crotch seam or inseam) first and then captured in the completion of the seam. We already talked about that in how I would put in the Peg Legs gusset a few posts back.
The Peg Legs gusset is set horizontally with the widest part of the diamond lined up with the crotch seams and the longer parts of the diamond extending down into each inseam:
I have also sewn in gussets in the past where the narrow ends of the gusset where lined up with the crotch seam and and widest parts at the inseam (imagine the image above with the diamond vertically). Unfortunately I can't show that to you as the pattern I used to use that had it done that way was an old Kwik Sew that has vanished from my collection and their catalogue.
By contrast to the diamond shape the Clara by Jalie has a smaller gusset, a sort of triangle set as an extension of the back crotch:
You can see here how it was first stitched to the bottom of the back crotch (I used a lightening stitch to do that) and then how it is captured when the back crotch is finally stitched. I am pretty sure that the explanation for the shape of this gusset is that the Clara's do not have a front crotch seam. The gusset as placed this way is finally stitched in via the one long seam ankle to ankle.
If you look at these two gussets you can see how they both add three dimensional space to the leggings right at a place that would just be a stress/vulnerable to stitching breaking place otherwise.
It also explains why gussets make leggings more comfortable.
I am sure you will also notice too that the diamond gusset is a larger unit and for that reason I suspect might give a little more movement room for a larger person. For this reason I chose the Peg Legs for my maternity leggings when I knew give was going to be important.
Gusset seams need to be topstitched.
This can be done with a cover hem or twin needle (see the Peg Legs gusset above) or a triple zig-zag like I did here in my Clara's, note the seam allowances are folded to the garment side and top stitched that way:
The point of this topstitching, here with a cover hem in a custom pattern (Greenstyle Creations and Jalie's Cora both have multiple seam options, is both to reinforce the seams (think of flat felling in jeans) as well as flatten the seams for comfort against the body.
But back to topstitching and conventional stitches. For topstitching gussets I always wind wooly nylon by hand onto a bobbin (a machine winds it too fast and stretches it out of shape) and this give wonderful stretch to any stitch.
For topstitching in a knit I generally like a multi-step zig zag rather than one that just zigs and zags because doing the zig in steps means there are not the long threads to catch.
Here is what a stitch made with the wooly nylon in the bobbin looks like, the underside of a three-step zig zag and both sides of a common utility stitch you could also use to topstitch seams if you really wanted to:
|three step zig-zag showing the bobbin side, bobbin hand wound with wooly nylon|
|Utility stitch right side on Supplex|
|Bobbin side of the same stitch showing how the wooly nylon stretches when stitched|
If you do decide to cover hem I personally think that a good fluffy wooly nylon is essential in the loopers. I also shorten the stitch length to about a 3 (I know many folks do a 4 but I like the extra stitches). You can do a two needle cover hem or a three needle.
Generally this is done from stitching from the wrong side so the loopers show decoratively on the right side, aiming to situate the stitches so they cover the well of the seam on the right side. This can actually be tricky to do, as is any dominant stitching that you do blind from the wrong side while hoping for the best. I have found that rather than trying aim for the centre of the seam try to put the middle needle of a 3 needle stitch or the centre of the space between the two needles of a two needle cover hem so it stitches right on top of the right hand needle/seam line of the garment's serged seam. This really helps getting it right.
3-needle cover hem from the right side:
And from the wrong side where hopefully you can see the middle needle set more or less to follow over the right hand needle seam thread of the serged seam:
To hem the leggings it is very important that they can be stretched to go over the foot without the stitches breaking, or, even more important in capri length leggings where the hem is over the large calf muscle that can expand with movement, without binding.
For this reason I always stretch a little while I topstitch the hems, to build in that extra stretch, whether I sew the hem with a 3 step zig zag with wooly nylon hand wound in the bobbin or with a narrow 2 needle cover hem, my preference to avoid tunnelling in these stretchy fabrics.
Below are two samples. You will see that the stitches in both hems looks small - this is because they were stretched when sewn and the extra stitches got packed in - something I wouldn't worry about in a hem at this level.
Finally the last detail in the construction of the leggings is the yoga band waistband.
There are several ways these can be done.
Some folks when working with a firmer knit like Supplex actually just sew the band and stitch it right on to the top of the leggings, counting on the double layer of fabric to provide both the stretch and support they need in a waistband without elastic. Others, and suggested in both patterns, also add a row of elastic only lightly stretched, to the seam allowance at the top of the band and band facing.
I have seen clear elastic suggested for this step, some sewers serge this into the seam that attaches both band layers, but I don't personally find that is feels secure enough inside the band.
My own preference is for a 1 / 2 " bathing suit elastic (you can recognize this for its boring muslin colour) that I triple zig zag stitch down to the inside of the band, butting the elastic right up to the seam like this:
Well this wraps up our leggings sew-along.
Not sure if I did this right. Suspect that there are more organized ways to run something like this so let me know if going through a garment type like this is helpful.
In future I am going to forget about the Facebook page I think hoped that there would be some pictures of works in progress from readers, but that was probably spreading us all too thin. I think this blog and my Instagram are more my own mediums in social media.
So for a bit the blog is going to resume regularly scheduled programming but watch this space once August kicks in for a bathing suit sew-along. Need to get that in before that awful moment when Nova Scotians start sniffing the air and saying things like " I can smell fall" and the back-to-school ads become depressingly frequent.
Around here we like to wring out every last drop of summer, and when we can't do that start packing the RV to head south!