In a country as large as the United States and one boasting as many law schools as it has, the attraction of ranking is almost irresistible. How else to make sense of the profusion? A sensitive and nuanced differentiation and description would tax critics' creative powers to bankruptcy. Not only, then, are law schools ranked, but law journals also. And here, too, it's the simple numbers that get used because . . . they're there, the most important measure being the frequency with which articles from the journal are cited by others (though whether the "others" must be published in journals other than the measured journal, I don't know).
Google has now joined this game — again, because the numbers exist and it has them. Google Scholar will offer you the "top" 20 publications (in English) in a variety of disciplines, including now law. The "metric" isn't a simple summation of all citations elsewhere, but the result of a more sophisticated arithmetic, the h-index:
The h-index of a publication is the largest number h such that at least h articles in that publication were cited at least h times each. For example, a publication with five articles cited by, respectively, 17, 9, 6, 3, and 2, has the h-index of 3.
As a consequence, Harvard Law Journal, with a h-index of 44, tops the list, bookended at number 20 by Notre Dame Law Review at a h-index of 30.
Robert Anderson has a couple of good blog posts about this, if you're interested in looking deeper. He's also created a ranking for individual law articles using citation data in Google Scholar. His ranking has the advantage of consulting all journals, not merely those that make the top 20, as Google's ranking of articles (i.e. not journals) does.
This last ranking — of articles — might be of general interest in that it suggests something about the intellectual topics that are involving legal scholars at the moment. And it will serve to introduce you to an interesting law blog.