Which WordPress themes are most widely used? That question is broad and difficult to answer. Luckily, there are related questions that are more focused and easier to answer. For example: which themes are most popular at WordPress.com? which have the most downloads from WordPress.org?
This post is about the answer to the first of these more specific questions. If I, as an admin of this or any other WordPress.com blog, browse themes I can request that the themes be ordered by popularity.
This is the current list of most popular themes at WordPress.com: ChaoticSoul, MistyLook, Ocean Mist, Cutline, Freshy, Black-LetterHead, Contempt, Ambiru, Digg 3 Column, Benevolence, Tarski, Andreas04, Solipsus, Blix, Rounded, and PressRow.
The first thing that struck me was the absence of Kubrick, which has been the default theme for new WordPress blogs for a while now. I suspect that there are indeed many Kubrick blogs, created but never really used, that the popularity algorithm excludes. I’ll add that Contempt is a close relative of Kubrick.
Second, it looks as though the typical popular theme has a custom header, and a sidebar on the right.
Third, only 3 or these 16 themes – Black-LetterHead, Tarski, and Blix – are currently in the free themes directory at WordPress.org. That’s unfortunate, since it’s particularly easy to install a theme from that directory at a self-hosted WordPress blog: you don’t need to leave the dashboard to use FTP.
I started looking into the initial question (Which WordPress themes are most widely used?) when I realized that using Typekit with WordPress is very theme-specific.