Modern domestic sewing machines are standardized, as far s I know, with stitch length expressed in mm. So, for example, 3 means an individual stitch length of 3mm. Pulling out my trusty little metal slide, I can see that 1 inch equals about 25mm, so a stitch length of 3 is equal to about 8 stitches per inch. I don't think this varies with brand, but maybe there are some exceptions out there.
I would have to pull out one of my vintage machines to check, but those machines may have stitch length expressed in number of stitches per inch (at least, in the U.S.). Seems to me I remember the settings being more like 8, 10, 12. This would be more in line with how hand stitches used to be counted.