Perhaps I have read this somewhere on HF but new in Sept and feeling a little overwhelmed with all the information I have looked at so far.
Is there a "go by" for a DIY whoopiesling in terms of how much amsteel to use if you want a certain length whoopie sling? Other variables may depend upon how long of a "constrictor" (right term?) you want, or the size of your fixed loop? I have both 7/64 and 1/8 and am just waiting for the right time to 'get after it'.
These instructions will get you close. Change the measurements and the dimensions change in the directions.
The directions do not include tapering the ends which should be done.
A basic rule for the slings is that they will be about half the distance of the length of the piece of Amsteel you start with. For example, if you had 10' of Amsteel, your resulting sling would be about 5' long. While the walkthrough above makes a 6' sling (by starting with a 12' length of Amsteel), I opted to make mine a little longer (7.5', used 15' of Amsteel) to have the option of hanging between trees that may be a bit farther apart.
As for the bury/constrictor, the closer the bury is to the fixed loop end (or end of the the hammock), the greater amount of length adjustment you will have. Mine is about 4" from the knot on the hammock, and my bury is 10" long. This basically gives me a whoopie sling that can adjust anywhere from about 16 inches min to 7.5 feet maximum. I'm not sure on a "proper" length of the bury, but 10" seems to be the generally understood safe/bulletproof length to ensure that the Amsteel properly constricts under weight and keeps you in the air. I've read posts about the bury being as small as 1", but if I were worried about an extra 9" of adjustment, I would just buy another 2 feet of Amsteel and be done with it. The safety is totally worth a few dollars in my opinion.
The fixed loop is optional, depending on what you're attaching it to. I put my slings on a GTUL with a channel end, so I just tied the Amsteel in a loop, put it through the channel and put a lark's head on it. I also didn't pretty up the loose ends on mine with backsplices. A double overhand knot works just fine as well. Keeping it simple was my priority this time around.
If you're worried about dimensions, the walkthrough I posted above should be more than enough to get you and hanging if you follow it word for word and measurement for measurement. It's a great place to start.
You can read about them until you're blue in the face, but once you make one things become a lot clearer. Plus, there's always the great people here who can help you out if you get confused.