What is the size of the プロフィール banner?

The way it shows up for me, it's 946 によって 250, give または take a few pixels. But I think there's もっと見る to it than that, because it adjusts itself to fit your browser. I 投稿されました link comparison of the critter sizes last night hoping for some tips on how to size it. I'm looking フォワード, 前進, 楽しみにして to making banners, too!