How do pixels(px) compare to points(pt) or inches in XSL-FO/FOP ?

[Hans Chicoine]

The context :   -I have a HTML document, a newsletter, formatted a bit like a newspaper's frontpage : blocks of text with arbitrary dimensions in arbitrary positions on the page. -Block dimensions are fixed (independant of text content) and specified in pixels. Texts in the blocks have there font sizes given in points (pt = 1/72). -I'm attempting the reproduce the same document in PDF using FOP.  I'd like everything in the PDF to be identical (at least proportional) to what it is in the HTML document.   The Problem :   In my XSL-FO stylesheet I've kept the same units : block dimensions in pixels(px) and font size in points(pt) ... BUT it is quite obvious in the rendered PDF that the ratios between block areas and the space taken up by the texts  ARE NOT the same in the HTML and in the PDF (typically more space is taken by the text in the PDF).   The question :   Would anyone know how to calculate a correction coefficient that reestablish the correct proportionality ? I suppose that that implies knowing how points are translated in pixels in a browser and how pixels are translated in absolute dimensions (eg. inches) in a xsl-fo renderer.     PS : I suppose I could specify block dimensions in inches in my HTML document ... but given the choice, I'd rather not do that.     Hope I'm Clear !   Hans