Hello Onomatopoetika,
I don’t think there is a size chart for this. After all, every calf circumference is different.
But I do have an idea:
measure the circumference of your upper arm, or your calf circumference. Based on that measurement, use a gauge swatch to calculate the stitches as if you were knitting in stockinette stitch. But then use that stitch count for a rib pattern, e.g. 2 knit stitches, 2 purl stitches alternating. It pulls together beautifully and is also very stretchy. And then, of course, it also depends on whether the leg warmers will be worn over pants or over leggings. That can add a few centimeters too - just measure it on yourself and, for a slimmer leg, use a few fewer stitches (for the rib pattern, 2 sts k, 2 sts p = divisible by 4).
Hope this helps.
I wrote a blog post about “gauge”; see here:
https://www.crazypatterns.net/de/blog/667/maschenprobe-umrechnen-so-geht-s