When using a scanner, the scanning resolution determines the size of
the scanned image
Use a resolution of 75 dots per inch (dpi) to get a life-size image
when displayed on the screens of most computers.
(26 KB file)
Scanning at a resolution of 150 dots per inch (dpi) gives an image that is
twice normal size and results in a much file size nearly four times larger.
(77 KB file)
Scanning at a resolution of 200 dots per inch (dpi) gives an
even larger file size (113 KB)

How to do it:
The scanning resolution is set in the scanner program. For example, in the
HP Precision Scan program, pull down the Settings menu, select Resolution...,
then type in the desired resolution in the designated place.