Opie did an excellent pictorial on how to make a continuous loop here:
I've had a lot of folks ask me if there was a simple formula for what length of line to use when making other than a 12" loop. Yes there is and let me just say this applies to 7/64" Amsteel Blue using the same 6" bury. So here we go...
(2 x L) + 12 +3 = inches of line needed. Where (L) is the length of the desired finished loop.
(12) is to account for the two 6" buries and (3) is to account for the compression of the outer line due to the buries.
You can simplify it to loop size times 2 plus 15 inches.
So if one wanted a 24" loop, you start with 63" of line. Again, this is for 7/64" Amsteel Blue.
Hope this helps those making loops.