This will depend on the font you're using. The column width setting is
the number of standard font numeric characters that fit into a cell,
while the row height is in points (where there are 72 points to an inch).
If your standard font is smaller or larger than the default, the 12.71
value will make the cells narrower or wider, respectively.
For instance, I use Verdana 10 pt as the standard font on my machine and
the width setting for exactly 1" is 9.57. Using 12.71 makes my cells 30%
wider than their height.
The only way currently to set column widths and row heights to the same
units is to use VBA, as Gord suggested.