The quilt pattern says use a stitch length of 12.
Your sewing machine says otherwise—there's anything from 0.0 to 6.0—but no '12'.
What's a quilter to do?
There are two ways we, quilters, use to describe stitch length.
Quite simply stated a setting of 12 stitches per inch is exactly that.
Your sewing machine lays down 12 stitches for every inch of fabric that is pulled through by the feed dogs.
Ponder that with this short story problem: My Juki DX-2000-QVP's maximum speed is 1,050 stitches/minute for a straight stitch. The stitch length is set to 12 stitches per inch (SPI).
That means in one minute you can sew a seam 1050 ÷ 12 = 87½"—that's a seam that's more than 2 YARDS long.
That's a lotta seam in a New York minute!
This is shown as a number usually with 1 decimal place, like 1.6. It refers to the actual stitch length.
So, a setting of 1.6 means each stitch is 1.6 millimeters long.
Now I've been sewing for over 50 years. Quilting for about half of that.
Egad! That's a long time. Since before I could cross the street by myself even...
...and while I can just about visualize what 12 spi looks like, I do have a wicked time picturing 2.2mm. (It figures—'m an American.)
They're the same.
So let's take the mystery out of converting between the two descriptions. Quilting shouldn't make your head hurt.
You start out knowing what the recommended spi (stitches per inch) or mm (millimeters) setting is for your project or the type of sewing you're doing.
The first thing to remember is there are 25.4mm in one linear inch.
Then it's a matter of simple division on your calculator using these formulas.
You know spi and want to find mm
The formula is:
25.4 ÷ spi = mm
You know mm and want to find spi
The formula is:
25.4 ÷ mm = spi
Easy peasy lemon squeezy!
Two things to watch out for.
Some machines are programmed in 0.1mm increments (1.1, 1.2, 1.3, etc.), while others are set in 0.5mm increments (1.0, 1.5, 1.5, etc.), others are somewhere in between.
Since it's your sewing machine, after doing the counting, why not take a Sharpie and mark it on your machine next to the appropriate stitch length icon so you don't have to remember it.
That's why you don't want to push or pull your fabric through your machine—you'll change the stitch length!
You are simply the guide.
For paper piecing a shorter stitch length helps perforate the paper and make it easier to remove. Anywhere from 16-20spi or 1.3-1.6mm.
For machine quilting with a walking foot somewhere from 8-12spi or 2.5-3.0mm.
For the micro stitching used to secure a machine quilted seam 24-30spi or 0.5mm. This stitching occurs at the beginning and end of a line of quilting.
For free motion quilting 0.0—there's no need to move the feed dogs at all because YOU are in charge depending on how fast or slow you move the quilt sandwich.
Notable exceptions—'cause there's always exceptions in quilting—if you're using a particularly fine, thin thread, use a shorter length. For a thicker thread, a longer stitch is called for.
The best way to fine tune it?
Try several settings on a practice quilt sandwich before beginning on your actual patchwork.
And finally, if you're using one of those luscious, sexy metallic or rayon threads, you'll want a longer one. The light needs something to reflect off for all that lusciousness to actually sparkle and shine.