Straight from the xlsgen web site:
Setting the width and height is possible on a per column and on a per row basis. It’s been exposed in the worksheet object for a while already (ColWidth, RowHeight, MultipleColWidth, MultipleRowHeight). With the Rows and Columns objects, it’s possible to do the same for a whole range of rows and columns at once, and more consistently. Units are different whether we are talking columns or rows. For columns, it’s a number of times a nominal character of size 8 points (rule of thumb : take a width in pixels, divide by 8). For rows, it’s pixels.
Google is your friend.
See more at http://xlsgen.arstdesign.com/core/rowsandcolumns.html