[BrianG]

The specs list it as:
59mm wide X 158mm long X 22mm thick.
Converting to inches is simply a matter of taking mm and dividing by 25.4. So, in inches:
2.32" wide X 6.22" long X 0.87" tall.
Since you are probably looking to make a battery tray, you want to estimate a little higher (and don't forget padding thickness if you use it). So, rounding the figures up a tad, that's:
2+3/8" wide X 6+1/4" long X 7/8" thick.

EDIT: jhautz beat me to it!