Quote Originally Posted by Sirius Glass View Post
As posted earlier, the best way is to line it by eye. There are no nifty formulae. To only guide line is that more room needs to be below the photograph than above because if above and below are equal, the eye and brain preceive the photograph as being too low and appearing to "slide off the bottom".

Steve, looking at the link John's just posted that's quite a neat guide that pretty much mirrors what we do visually.