I think I know where Jcrich is coming from.  If you were going purchase or gather enough supplies to back a bow how much is enough.  In other words would six white tail deer leg tendons make two layers, or one, three or not even one?  I would be interested in the answer to that.  Knowing how many layers for the length is good information and I am glad this thread went there.  Just looking for a bit more.  
I had a similar question about sinew string and found that it takes about one to one and half WT deer back strap tendons to make a sinew bowstring about 48" long.  Of course the size of the deer matters and will make the number fluctuate.  However, 2 back strap tendons should be enough.