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.

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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

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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