diff --git a/ChangeLog b/ChangeLog
index 6f7ebddb05..222f322cf1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed May 18 22:45:26 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/io/console/lib/console/size.rb (IO#console_size): new
+	  method.  (EXPERIMENTAL)
+
 Wed May 18 22:41:51 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* internal.h: add for internal use only.
diff --git a/ext/io/console/lib/console/size.rb b/ext/io/console/lib/console/size.rb
new file mode 100644
index 0000000000..e9d8a1fbb6
--- /dev/null
+++ b/ext/io/console/lib/console/size.rb
@@ -0,0 +1,20 @@
+def IO.default_console_size
+  [
+    ENV["LINES"].to_i.nonzero? || 25,
+    ENV["COLUMNS"].to_i.nonzero? || 80,
+  ]
+end
+
+begin
+  require 'io/console'
+rescue LoadError
+  class IO
+    alias console_size default_console_size
+  end
+else
+  def IO.console_size
+    console.winsize
+  rescue NoMethodError
+    default_console_size
+  end
+end