[pdftex] question

[Walt Burkhard]

I have just begun using pdftex and note the size of the output is smaller 
than the output produced via postscript.  That is, I can print either the
xxx.pdf via acroread or xxx.ps  and the pdf output is slightly smaller.
The text file is plain tex without magnification operations.
The composition/typography remains evidently unchanged.  Here are a few
sample measurements:
	ps:	top of text to bottom of page number is 9 3/4 inches
		top of text to bottom of text is 8 13/16 inches

	pdf:	top of text to bottom of page number is 8 7/8inches
		top of text to bottom of text is 8 1/16inches

What can I do to get these two outputs to appear to be the same?

Thanks in advance.

Walt Burkhard