This is a pair of PDFs (one US Letter size, one A4) that you can print out in order to measure the width and height of anything smaller than a page.

Make sure you print the PDF at exactly 100% scale. Don't use “Scale to Fit Page” or anything similar. Otherwise, your centimeters will not be true centimeters.

Here's what it looks like in use:

The PostScript (.ps) files are the source code. If you know PostScript, you can edit the grid-generating machinery or make your own paper sizes.

If you do edit the source, use make to regenerate the PDFs. You'll need to have pstopdf installed; theoretically, either Ghostscript's or Apple's should work, though I've only tried Apple's. If you add any other paper sizes, you will need to add them to the Makefile.

The license is a typical BSD license. See LICENSE.txt for details.