You can try this graph paper template with 3 sizes from the MS Template Gallery.

http://office.microsoft.com/en-us/templates/TC010183751033.aspx?pid=CT101448201033

Note:  the actual size will depend upon your resolution.

If not satisfactory try this method...........

If you want to use VBA to set height and width in mm which you can convert to
inches............

Ole Erlandson has code for setting row and column dimensions.

http://www.erlandsendata.no/english/index.php?d=envbawssetrowcol

Gord Dibben Excel MVP