Comment 81 for bug 29622

Re: to Comment #51:

To be precise, one can get the PPD file by using the cupsGetPPD() function:
http://www.cups.org/documentation.php/api-cups.html#cupsGetPPD

And the needed info can be extracted from this PPD using proper PPD-related functions:
http://www.cups.org/documentation.php/api-ppd.html#ppdPageSize

If I understand this correctly, one will receive a struct that describes (among others) the printable area:

struct ppd_size_s
{
  float bottom; // Bottom printable margin in points
  float left; // Left printable margin in points
  float length; // Length of media in points
  int marked;
  char name[PPD_MAX_NAME];
  float right; // Right printable margin in points
  float top; // Top printable margin in points
  float width; // Width of media in points
};

There are lots of working examples of the usage of those functions in open source software:
http://www.google.com/codesearch?q=ppdPageSize+cupsGetPPD