Do not measure, measuring is the least likely to give you identification help.
Start with the perforations. This stamp is 10.5 x 11 so it can only be #632. This is also a Washington/franklin which can quick be identified by color; the yellow green hue will always be a #632.http://stampsmarter.com/1847usa/192...ntifier.html
Lastly, always assume that you have the most common stamp variety. If you found a lottery ticket on the ground, you would not assume that you had just won the mega-lottery. The same applies to stamps; they printed billions of the common varieties; the odds are better that you would get hit by lightning twice in the same day than finding one of the rare varieties.