Found via Starjewel:

The following charts maps shoes sizes in different units used around the world (inches, centimeters, American, British, Japanese, and European shoes sizes) to the lengths of men’s units (in inches and centimeters).

Would this be a good time to mention I’m a 9-1/2 wide? Maybe not, as the page goes on to say,

As for shoe widths, there isn’t enough information about shoe widths to create the corresponding mapping to penis widths.

Ah well. Anyway, without further ado, here you go…
Shoe/Penis Size Conversions