I have several sewing machines and if you’re a quilter, maybe you do, too. When it comes to stitch length, some machines use a metric length such as 2.5 or 3.0. This tells you that each stitch is 2.5 or 3.0 millimeters long.
Other machines use an English stitches-per-inch setting such as 12 or 15 or 20. This tells you that in every inch of a seam, there are that many stitches. Setting stitch length to 15 means there will be 15 stitches in every inch.
This post is to explain how you can convert from metric stitch length to stitches-per-inch, or visa versa.