What are they telling me is the gauge? It says 10 cm x 10 cm (that's 4 x 4 inches, right? ) then it says 26 R (that's 26 rows?) and 20 M. Not sure what the "M" means, but assuming that is the measure across, are they saying that this gauge is 5-6 st/inch.
10cm is not exactly 4 inches but they use them as though they were the same on international gauge information. The R would be rows all right and the M is the first letter of the word stitches in some other language (I can't remember which language right now), so that is the number of stitches in 4 inches--20. 26 rows make 4 inches and 20 stitches make 4 inches, using whatever needle works for you, and it is usually in the range of 3-5 for most people.
But that is all what the yarn usually is worked to. What about the pattern you are using, or are you using one? You would need to find a sock pattern with near this gauge, maybe a little smaller, because socks are often knit tightly.
12 inches(that is calf, what about the ankle?) would work out to be 60 stitches all right with the gauge given. Ribbing will have a lot of stretch, and cling. But I'm still thinking about that pattern. It seems a pattern for your first pair of socks would be a good idea.