Figuring out the print size of a photo at 300 DPI

I was looking for an easy way to tell the print size of a photo at 300 DPI. It wasn't as easy to find the answer as I'd expected. For future reference, here's a solution using ImageMagick:

identify -format "%[fx:w/300*2.54] x %[fx:h/300*2.54] cm" photo.jpg