It's not really comparable due to every artist studying differently, but it would work for oneself. I will probably do this once every 6 months due to it being a real pain lol. it would be great to compare with others but it would be impossible to manage :P
Basically each skill (hands, faces, body, hair) is split up, and the amount you have done is counted. so for example, Lego has done 1000 hands. each skill levels up on a power of 2, so 2,4,8,16,32 and so on. that means his hands skill is at level 9, soon to become 10 (2^10 being 1024) (I think)
your artist level is either based on the average of all your skills, or you gain 1 point for every level of every skill, with the same 2,4,8 level boundaries.
This doesn't measure skill, but output, but since these are heavily linked I think it's worth a count. shame it's such a pain to measure. each level boundary being double is a reminder that you have to put in a lot of effort to significantly improve from the level you are at, and it's noticeable which area you haven't done much work in.
maybe double is too much but you get the idea.
I made this stupidly the other day on a high but forgot to post it and now I've reminded myself. based on the 10000 hour mastery but not actually related since I sketch a page in 25 minutes average :P
I wanted to do this again but with the levels thing I said above.
red and blue for HP and MP obviously :P
EDIT: here's a mini cool random mockup that would work as a profile image/signature (just about, given the tiny profile images)
If only I could put as much effort into things that mattered like manga lol