What are PDFs measured in?

I'm using iTextSharp to apply开发者_高级运维 rectangles to a PDF. It uses XY coordinates. I was wondering what type of measurement does PDF use? I know in Access uses twips for example.

Measurements are in PDF units:

The PDF specification defines space in a PDF file such that 72 PDF units is equal to 1 inch. Therefore, an 8 1/2" x 11" page would convert to 612 PDF units by 792 PDF units.

You might also want to read up on the PDF coordinate system

Apparently PDF has it's own measurements.

72 PDF units is equal to 1 inch

See this link for conversion to inches: http://www.activepdf.com/support/knowledgebase/view.cfm?tk=dc&kb=11867