Hard to tell, but that tarp in the image does not look all that big. I would guesstimate it to be at the smallest, a 6x8' or at the largest, 6x10'. Either size is too small to be much use in providing an adequate and walled shelter from rain, wind, bugs etc without some serious work.
You are probably right, 6x8. Found it here http://stormprepare.com/Tarp.htm I hoped it's at least the one pictured above it on that shopping list..., still, you cannot make a raft out of a tent:
By the way, another wonder from the same russian guy, where instead of tarp he is using the polyethylene wrapping film.
2000' of that can be had for just $15, and provide a lot of interesting options, including quite a nice shelter:
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